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THE WORMAN SERIES 1 MODE RN LANGDA&E, 

k Complete Course in German. 

By JAMES H. WORMAW, A.M. 

EMBKACma 

gj-e;riwla.is3- reader,, 

O-ERMi^nS" ECHO. 

IN PKBPABATION, 

HISTORY Oir» GJ^ERMLA^N- IL.ITERj5k^TXJJaE, 

G-ERM:-A.N^ ^I<rD ETsTG^LISH IL.EXICON-. 

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III. waHMAN'S GJEIt3IAIi^ ECHO {Deutsches Echo) is entirely a new 
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No other method will ever make the student at home in a foreign language. By this 
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through. The laborious process of translating his thoughts no longer impedes free 
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FOURTEEN WEEKS COURSE 



rN^ 



DESCRIPTIVE ASTRONOMY. 



BY 

JPDORMAN STEELE, Ph. D., 

PRINCIPAL OF ELMIRA FREE ACADEMY, 

Author of " A Fourteen Weeks Course in Chemistry.' 



" The heavens declare the glory of God ; and the firmament showeth his 
landy-work." Psalm xix. 1. 



NEW YORK: 

A. S. BARNES & Co., Ill & 113 WILLIAM STREET. 

BOSTON : 

WOOLWORTH, AINSWORTH & Co. 

1870. 



IMPORTANT ANNOUi>( CEMENT. 



FOURTEEN WEEKS 



ALL THE SCIENCE S 

BY 

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having but a limited period to give to these branches. Th ey 
are especially adapted to Public and High Schools. 

I.— Fourteen "Weeks in Natural Philosophy. . .$1 50 

II. — Fourteen "Weeks in Chemistry 1 25 

III. — Fourteen "Weeks in Astronomy (with chart). 1 50 

I"V. — Fourteen "Weeks in Geology. In preparation. 1 75 

V. — Steele's Ans. to Questions and Problems 1 50 

VI. — Elements of Physiology. Jarvis 75 

VII. — Object Lessons in Botany'. Wood 1 50 

VIII. — Chambers' Elements of Zoology 1 50 

These books will be found, as soon as issued, at all tiie 
leading bookstores in the United States, or will be forwarded 
by the publishers by mail, postpaid, on receipt of price. 

A^. S>*O^Il.]VEJS &: CO., 
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Entered according to Act of Congress in the year 1869, 
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to thft, Clerk's Office of the United Statea District Court for the Southern District of New 1 < 

Olft 



Hennen Jennings 
April 26, 1933 



PREFACE. 



During tlie past few years great advances have 
been made in astronomical science. A new hori- 
zontal parallax of the sun has been established. 
This has materially altered the estimated distances, 
etc., of the planets. The sun is much nearer us than 
we supposed, and light has lost a little of its wonder- 
ful velocity. Much additional information has been 
obtained concerning Meteors and Shooting Stars. 
The investigations connected with Spectrum Analy- 
sis have been especially suggestive. Thus on every 
hand the facts of Astronomy have been accumulat- 
ing. As yet, however, they are scattered through 
many expensive foreign works, and are consequently 
beyond the reach of most of our schools. It has 
been the aim of the author to collect in this little 
volume the most interesting features of these larger 
works. Believing that Natural Science is full of fas- 
cination, he has sought to weave the story of those 
far-distant worlds into a form that may attract the 
attention and kindle the enthusiasm of the pupil. 
The work is not written for the information of scien- 
tific men, but for the inspiration of youth. The 
pages therefore are not burdened with a multitude 



6 PREFACE. 

of figures which no memory could possibly retain. 
Mathematical tables and data, Questions for Re- 
view, and also a Guide to the Constellations, are 
given in the Appendix, where they may be useful 
for constant reference. 

The author would call particular attention to the 
method of classifying the measurements of Space, 
and the practical treatment of the subjects of 
Parallax, Harvest Moon, Eclipses, the Seasons, 
Phases of the Moon, Time, Nebular Hypothesis, 
&c. 

To teachers heretofore compelled to use a cum- 
bersome set of charts, it is hoped that the star maps 
here offered will present a welcome substitute. The 
geometrical figures showing the actual appearance 
of the constellations, will relieve the mind confused 
with the idea of numberless rivers, serpents, and 
classical heroes. The brightest stars only are given, 
since in practice it is found that pupils remember 
the general outlines alone. 

Finally, the author commits this Httle work to 
the hands of the young, to whose instruction he has 
consecrated the energies of his life, in the earnest 
hope that, loving Nature in all her varied phases, 
they may come to understand somewhat of the wis- 
dom, power, beneficence, and grandeur displayed in 
the Divine harmony of the Universe. 

" One God, one law, one element, 

And one far-off Divine event 

To wMcli the whole creation moves." 



PKEFACE. 7 

The following works, among others, have been Ireely con- 
sulted in preparing this volume : 

The Heavens Guillemin. 

Astronomy Chambers. 

Introduction to Astronomy Hind. 

Solar System Hind. 

Popular Asti'onomy Airy. 

Popular Astronomy Arago, 

Astronomy Norton. 

Asti'onomy Robinson. 

Astronomy Loomis. 

Age of Fable Bulfinch. 

Poetry of Science Hunt. 

Outlines of Astronomy Herschel. 

Popular Astronomy Mitchell. 

Astronomy and Physics Whewell. 

Annual of Scientific Discovery Kneeland 

The Chemical News. 



SUGGESTIONS TO TEACHERS. 



This Tvork is designed to be recited in the topical method. 
On naming the title of a paragraph, the pupil should be able to 
draw on. the blackboard the diagram, if any is given, and state 
the substance of what is contained in the book. It will be 
noticed that the order of topics, in treating of the planets and 
also of the constellations, is uniform. If a portion of the class 
vnite then* topics in full upon the blackboard, it will be found 
a valuable exercise in spelling, punctuation, and composition. 
Every point which can be illustrated in the heavens should be 
shown to the class. No description or apparatus can equal the 
reality in the sky. After a constellation has been traced, the 
pupil should be practised in star-map drawing. Much profit- 
able instruction can be obtained in this way. For the pur- 
pose of more easily finding the heavenly bodies at any time, 
Whit all's Movable Planisphere is of great service. It 
may be procm-ed of the publishers of this work. " Orreries 
are of little account." A tellurian is invaluable in explaining 
Precession of the Equinoxes, Eclipses, Phases of the Moon, etc. 
Messrs. J. Nellegar & Co., Albany, N. Y., furnish a good instru- 
ment at a low price. The article on " Celestial Measm-ements," 
near the close of the work, should be constantly referred to dur- 
ing the term. In the figures, the right-hand side represents the 
west and the left-hand the east. When it is important to obtain 
this idea correctly, the book should be held up toward the south- 
em sky. 



TABLE OF CONTENTS. 



CELESTIAL MAP. 

L INTRODUCTION. 

PAGB 

HISTORY OF ASTRONOMY i6 

SPACE .35 

THE THREE SYSTEMS OF CIRCLES ... 37 

II. THE SOLAR SYSTEM . . 43 

THE SUN 46 

THE PLANETS 65 

Vulcan • 82 

Mercury 83 

Venus 89 

The Earth 96 

The Seasons . . . . . . .110 

Precession and Nutation . . .120 
Refraction, Aberration and Parallax . 130 

The Moon 139 

Eclipses 155 

The Tides ....... 165 

Mars 168 

The Minor Planets . . . .172 

Jupiter .... ... 175 

Saturn . . . . . . . .182 

Uranus ...... .189 

Neptune 191 

METEORS AND SHOOTING STARS . .194 



12 TABLE OF CONTENTS. 

PAGE 

COMETS 206 

ZODIACAL LIGHT 217 



IIL THE SIDEREAL SYSTEM . . 219 

THE STARS 221 

THE CONSTELLATIONS 234 

Northern Circumpolar Constellations . 234 
Equatorial Constellations .... 242 
Southern Constellations .... 263 

DOUBLE STARS, COLORED STARS, VARIABLE 
STARS, CLUSTERS, MAGELLANIC CLOUDS, 
NEBULA, &C. ...... . 265 

THE MILKY WAY . . . . . . 280 



THE NEBULAR. HYPOTHESIS . . . .282 

CELESTIAL CHEMISTRY.— Spectrum Analysis 284 

TIME 288 

CELESTIAL MEASUREMENTS .... 298 

APPENDIX 311' 

Tables 312 

Questions . . . . . . . .315 

Guide to the Constellations . . .331 

Index . • 335 



/ 



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H 



INTRODUCTION. 



Astronomy (astron, a star, and 7iomos, a law) treats 
of the Heavenly Bodies — the sun, moon, planets, 
stars, and, as our globe itself is a planet, of the 
earth also. It is, above all others, a science that 
cultivates the powers of the imagination. Yet all 
its theories and distances are based upon the most 
rigorous mathematical demonstrations. Tl^.us the 
study has at once the beauty of poetry and the ex- 
actness of Geometry. 

The Appearance of the Heavens to an Observer. — 
The great dome of the sky filled with glittering 
stars is one of the most sublime spectacles in nature. 
To enjoy this fully, a night must be chosen when 
the air is clear, and the moon is absent. "We then 
gaze upon a deep blue, an immense expanse studded 
with stars of varied color and brilliancy. Some 
shine with a vivid light, perpetually changing and 
twinlding; others, more constant, beam tranquilly 
and softly upon us ; while many just tremble into 
our sight, like a wave that, struggling to reach some 
far-off land, dies as it touches the shore. In the 
presence of such weird and wondrous beauty, the 



14 INTBODUGTION. 

tenderest sentiments of the heart are aroused — a 
feehng of awe and reverence, of softened melan- 
choly mingled with a thought of God, comes over 
us, and awakens the better nature within us. Those 
far-off hghts seem full of meaning to us, could we 
but read their holy message ; they become real and 
sentient, and, like the soft eyes in pictures, look lov- 
ingly and inquiringly upon us. We come into com- 
munion with another life, and the soul asserts its 
immortahty more strongly than ever before. "We 
are humbled as we gaze upon the infinity of worlds, 
and strive to comprehend their enormous distances, 
their magnificent retinue of suns. The powers of 
the mind are aroused, and eager questionings crowd 
upon us. What are those gUttering fires? What 
their distances from us ? Are they worlds like our 
own ? Do living, thinking beings dwell upon them ? 
Are they carelessly scattered through infinite space, 
or is there an order of the universe ? Can we ever 
hope to fathom those mysterious depths, or are they 
closed to us forever ? Many of these problems have 
been solved ; others yet await the astronomer whose 
keen eye shall be strong enough to read the myste- 
rious scroll of the heavens. Two hundred genera- 
tions of study have revealed to us such startKng 
facts, that we wonder how man in his feebleness 
can grasp so much, see so far, and penetrate so 
deeply into the mysteries of the universe. Astron- 
omy has measured the distance of many of the stars, 
and of all the planets ; computed their weight and 



INTKODUCTION. 15 

size, their days, years, and seasons, with many of 
their physical features ; made a map of the moon, in 
some respects more perfect than any map of the 
earth ; tracked the comets in their immense sidereal 
journeys, marking their paths to a nicety of which 
we can scarcely conceive, and at last it has analyzed 
the structure of the sun and far-off stars, announ- 
cing the very elements of which they are composed. 
Observing for several evenings those stars which 
shiue with a clear distinct light, we notice that they 
change their position with respect to the others. 
They are therefore called *' planets'' (Hterally, wan- 
derers). Others remain immovable, and shine with 
a shifting, twinkling light. They are termed the 
"fixed stars" although it is now known that they 
also are in motion — the most rapid of any known 
even to Astronomy — ^but through such immense or- 
bits that they seem to us stationary. Then, too, 
diagonally girdling the heavens, is a whitish, vapory 
belt — ^the Milhy Way. This is composed of multi- 
tudes of millions of suns — of which our own sun 
itseK is one — so far removed from us that their light 
mingles, and makes only a fleecy whiteness. This 
magnificent panorama of the heavens is before us, 
inviting our study, and waiting to make known to us 
the grandest revelations of science. 



15 INTEODUCTION. 



DESCRIPTIVE ASTRONOMY. 



HISTOKY. 



Astronomy is the most ancient of all sciences. 
The study of the stars is doubtless as old as man 
himself, and hence many of its discoveries date back 
of authentic records, amid the dim mysteries of tra- 
dition. In tracing its history, we shall speak only 
of those prominent facts which will best enable us to 
understand its progress and glorious achievements. 

The Chinese. — This people boast much of their 
astronomical discoveries. Indeed their emperor 
claims a celestial ancestry, and styles himself " Son 
of the Sun." They possess an account of a conjunc- 
tion of four planets and the moon, which must have 
occurred a century before the Flood. They have 
also the first record of an ecHpse of the sun, which 
took place about two hundred and twenty years* after 
the Deluge. It is reported that one of their kings, 
tv/o thousand years before Christ, put to death the 
principal officers of state because they had failed to 
calculate an approaching eclipse. 

* October 13, 2127 b. c. 



HISTOBY. 17 

The Chaldeans. — Tli© Chaldean shepherds, watch- 
ing their flocks by night under the open sky, could 
not faU to become familiar with many of the move- 
ments of the heavenly bodies. When Alexander 
took Babylon, two centuries before Christ, he found 
in that city a record of their observations reaching 
back about nineteen centuries, or nearly to the con- 
fusion of tongues at the Tower of Babel. The 
Chaldeans divided the day into twelve hours, in- 
vented the sun-dial, and also discovered the "Saros" 
or "Chaldean Period," which is the length of time 
in which the echpses of the sun and moon repeat 
themselves in the same order. 

The Gkecians. — In the seventh century b. c. 
Tholes, noted for his electrical discoveries, acquired 
much renown, and established the first school of 
Astronomy in Greece. He taught that the earth is 
round, and that the moon receives her light from 
the Sim. He introduced the division of the earth's 
surface into zones, and the theory of the obliquity 
of the ecliptic. He also predicted an echpse of the 
sun which is memorable in ancient history as having 
terminated a war between the Medes and Lydians. 
These nations were engaged in a fierce battle, but 
the awe produced by the darkening of the sun was 
so great, that both sides threw down their arms and 
made peace. Thales had two pupils, Anaximander 
and Anaxagoras. The first of these taught that the 
stars are suns, and that the planets are inhabited. 
He erected the fir>st sun-dial, at Sparta. The secoud 



18 INTKODUCTION. 

iDaintained that there is but one God, that the sun 
is solid, and as large as the country of Greece, and 
attempted to explain echpses and other celestial 
phenomena by natural causes. For his audacity 
and impiety, as his countryman considered it, he 
and his family were doomed to perpetual banish- 
ment. 

Pythagoras founded the second celebrated astro- 
nomical school, at Crotona, at which were educated 
hundreds of enthusiastic pupils. He knew the 
causes of echpses, and calculated them by means of 
the Saros. He was most emphatically a dreamer. 
He conceived a system of the universe, in many re- 
spects correct ; yet he advanced no proof, and made 
few converts to his views, and they were soon well- 
nigh forgotten. He held that the sun is the centre 
of the solar system, and that the planets revolve 
about it in circular orbits ; that the earth revolves 
daily on its axis, and yearly around the sun ; that 
Yenus is both morning and evening star ; that the 
planets are inhabited — and he even attempted to 
calculate the size of some of the animals in the 
moon ; that the planets are placed at intervals cor- 
responding to the scale in music, and that they move 
in harmony, making the "music of the spheres," 
but that this celestial concert is heard only by the 
gods — the ears of man being too gross for such 
divine melody. 

Eudoxus, who lived in the fourth century b. c, in- 
vented the theory of the Crystalline Spheres. He 



HISTORY. 19 

held that the heavenly bodies are set, like gems, in 
holloAV, transparent, crystal globes, which are so 
pure that they do not obstruct our view, while they 
all revolve around the earth. The planets are 
placed in one globe, but have a power of moving 
themselves, under the guidance — as Aristotle taught 
— of a tutelary genius, who resides in each, and 
rules over it as the mind rules ove^ the body. 

HipparcJius, who flourished in the second century 
B. c, has been called the " Newton of Antiquity." 
He was the most celebrated of the Greek astrono- 
mers. He calculated the length of the year to with- 
in six minutes, discovered the* precession of the equi- 
noxes, and made the first catalogue of the stars — 
1081 in number. 

The Egyptians. — Egypt, as well as Chaldea, was 
noted for its knowledge of the sciences long before 
they were cultivated in Greece. It was the practice 
of the Greek philosophers, before aspiring to the 
rank of teacher, to travel for years through these 
countries, and gather wisdom at its fountain-head. 
Pythagoras spent thirty years in this manner. Two 
hundred years after Pythagoras, the celebrated 
school of Alexandria was established. Here were 
concentrated in vast libraries and princely halls 
nearly all the wisdom and learning of the world. 
Here flourished all the sciences and arts, under the 
patronage of munificent kings. At this school Ptol- 
emy, a Grecian, wrote his great work, the "Alma- 
gest," which for fourteen centuries was the text- 



20 INTEODUCTION. 

book of astronomers. In this work was given what 
is known as the "Ptolemaic System." It was 
founded largely upon the materials gathered by 
previous astronomers, such as Hipparchus, whom 
we have already mentioned, and Eratosthenes, who 
computed the size of the earth by the means even 
now considered the best — the measurement of an 
arc of the meridian. 

Ptolemaic Theoey. — The movements of the planets 
were to the ancients extremely complex. Yenus, for 
instance, was sometimes seen as " evening star" in 
the west, and then again as " morning star" in the 
east. Sometimes she deemed to be moving in the 
same direction as the sun, then going apparently 
behind the sun, appeared to pass on again in a 
course directly opposite. At one time she would 
recede from the sun more and more slowly and 
coyly, until she would appear to be entirely station- 
ary; then she would retrace her steps, and seem 
to meet the sun. All these facts were attempted 
to be accounted for by an incongruous system of 
" cycles and epicycles," as it is called. The advo- 
cates of this theory assumed that every planet re- 
volves in a ckcle, and that the earth is the fixed 
centre around which the sun and the heavenly bodies 
move. They then conceived that a bar, or some- 
thing equivalent, is connected at one end with the 
earth ; that at some part of this bar the sun is at- 
tached ; while between that and the earth, Yenus is 
fastened — not to the bar directly, but to a sort of 



HISTORY. 21 

crank ; and furtiier on, Mercury is hitched on in the 
same way. In the cut, let A be the earth, S the sun, 
ABDF the bar (real or imaginary), BC the short 
bar or crank to which Yenus is tied, T> E another 
bar for Mercury, F G another bar, with still another 
short crank, at the end of which, H, Mars is attached. 




THE PTOLEMAIC THEOKT. 

Thus they had a complete system. They did not 
exactly understand the nature of these bars — 
whether they were real or only imaginary — but they 
did comprehend their action, as they thought ; and 
so they supposed the bar revolved, carrying the sun 
and planets along in a large circle about the earth ; 
while all the short cranks kept flying around, thus 
sweeping each planet through a smaller circle. By 
this theory, we can see that the planets would 
sometimes go in front of the sun and sometimes 
behind; and their places were so accurately pre- 
dicted, that the error could not be detected by the 
rude instruments then in use. As soon as a new 
motion of one of the heavenly bodies Avas discov- 
ered, a new crank, and of course a new circle, was 



22 INTEODUCTION. 

added to account for the fact. Thus the system 
became more and more complicated, until a com- 
bination of five cranks and circles was necessary to 
make the planet Mars keep pace with the Ptolemaic 
theory. No wonder that Alfonso, king of Castile, 
and a very celebrated patron of Astronomy, revolted 
at the cumbersome machinery, and cried out, "If 
I had been consulted at the creation, I could have 
done the thing better than that !" 

AsTEOLOGY. — After the death of Ptolemy, Astron- 
omy ceased to be cultivated as a science. The 
Romans, engrossed with schemes of conquest, never 
produced a single great astronomer. Indeed, when 
Julius Caesar reformed the calendar, he obtained the 
assistance, not of a Roman, but of Sosigenes an Alex- 
andrian. The Arabians studied the stars merely for 
purposes of soothsaying and prophecy. They pro- 
fessed to foretell the future by the appearance of the 
planets or stars. All of the ancient astronomers 
shared more or less in this superstition. Tiberius, 
emperor of Rome, practised Astrology. Hippoc- 
rates himself, the " Father of Medicine " who flour- 
ished in the 4th century B. C, ranked it among the 
most important branches of knowledge for the phy- 
sician. Star-diviners were held in the greatest 
estimation. The system continued to increase in 
credit until the Middle Ages, when it was at its 
height of popularity. The issue of any important 
undertaking, or the fortunes of an individual, were 
foretold by the astrologer, who drew up a Horoscope, 



HISTOEY. 23 

representing the position of the stars and planets at 
the beginning of the enterprise, or at the birth of 
the person. It was a complete and complicated 
system, and contained regular rules, which guided 
the interpretation, and which were so abstruse 
that the J required years for their entire mastery. 
Yenus foretold love ; Mars, war ; the Pleiades,* 
storms at sea. The ignorant were not alone the 
dupes of this visionary system. Lord Bacon be- 
lieved in it most firmly. As late even as the reign 
of Charles II., Lilly, a famous astrologer of that 
time, was called before a committee of the House of 
Commons to give his opinion on the probable issue 
of some enterprise then under consideration. How- 
ever foolish the system of Astrology itself may have 
been, it preserved the science of Astronomy during 
the Dark Ages, and prompted to accurate observa- 
tion and diligent study of the heavens. 

The Copernican System. — About the middle of 
the sixteenth century, Copernicus, breaking away 
from the theory of Ptolemy, which was still taught 
in all the institutions of learning in Europe, revived 
the theory of Pythagoras. He saw how beautiful- 
ly simple is the idea of considering the sun the 
grand centre about which revolve the earth and all 
the planets. He noticed how constantly, when we 
are riding swiftly, we forget our own motion, and 
think that the trees and fences are ghding by us in 



PlC'-ya-d5z. 



24 INTRODUCTION. 

the contrary direction. He applied tliis tliouglit to 
the movements of the heavenly bodies, and main- 
tained that, instead of all the starry host revolving 
about the earth once in twenty-four hours, the earth 
simply turns on its own axis : that this produces 
the apparent daily revolution of the sun and stars ; 
while the yearly motion of the earth about the sun, 
transferred in the same manner to that body, would 
account for its various movements. Though Coper- 
nicus thus simplified so greatly the Ptolemaic the- 
ory, he yet found that the idea of circular orbits for 
the planets would not explain all the phenomena ; 
he therefore still retained the " cycles and epicycles" 
that Alfonso had so heartily condemned. For forty 
years this illustrious astronomer carried on his ob- 
servations in the upper part of a humble, dilapi- 
dated farm-house, through the roof of which he had 
an unobstructed viev/ of the sky. The work con- 
taining his theory was at last pubKshed just in time 
to be laid upon his death-bed. 

Tycho Beah ', a celebrated Danish astronomer, 
next propounded a modification of the Copernican 
system. He rejected the idea of cycles and epi- 
cycles, but, influenced by certain passages of Scrip- 
ture, maintained, with Ptolem}^, that the earth is the 
centre, and that all the heavenly bodies revolve 
about it daily in circular orbits. Brahe was a noble- 
man of wealth, and, in addition, received large sums 
fi'om the Government. He erected a mag-nificent 
observatory, and made many beautiful and rare in- 



HISTORY. 25 

struments. Clad in his robes of state, he watched 
the heavens with the intelligence of a philosopher 
and the splendor of a king. His indefatigable in- 
dustry and zeal resulted in the accumulation of a 
vast fund of astronomical knowledge, which, how- 
ever, he lacked the wit to apply to any further ad- 
vance in science. His pupil, Kepler, saw these facts, 
and in his fruitful mind they germinated into three 
great truths, called Kepler's laws. These constitute 
almost the sum of astronomical knowledge, and form 
one of the most precious conquests of the human 
mind. They are the three arches of the bridge over 
which Astronomy crossed the gulf between the Ptol- 
emaic and Copernican systems. 

Kepler's Laws. — Kepler, taking the investigations 
of his master, Tycho Brahe, determined to find what 
is the exact shape of the orbits of the planets. He 
adopted the Copernican theory, that the sun is 
the centre of the system. At that time all be- 
heved the orbits to be circular. Since, as they said, 
the circle is perfect, is the most beautiful figure in 
nature, has neither beginning nor ending, therefore 
it is the only form worthy of God, and He must 
have used it for the orbits of the worlds He has 
made. Imbued with this romantic view, Kepler 
commenced with a rigorous comparison of the 
places of the planet Mars, as observed by Brahe, 
with the places^ as stated by the best tables that 
could be computed on the circular theory. For a 
time they agreed, but in certain portions of the 

2 



26 



INTEODUCTION. 



orbit tlie obseryations of Brahe ^-ould not fit tlie 
computed place by eight minutes of a degTee. Be- 
lieying that so good an astronomer could not be 
mistaken as to the facts, Kepler exclaimed, " Out of 
these eight minutes we will construct a new theory 
that will explain the movements of all planets." He 
resumed his work, and for eight years continued to 
imagine every conceivable hypothesis, and then pa- 
tiently to test it — "hunt it down," as he called it. 
Each in turn proved false, until nineteen had been 
tried. He then determined to abandon the cii'cle 
and ado]3t another form. The eUiyse suggested itself 
to his mind. Let us see how this figure is made. 



Fii. 2. 




Attach a thread to two pins, as at F F in the 
figure ; next move a pencil along with the thread, 
the latter being kept tightly stretched, and the point 
wiU mark a curve which is flattened in proportion 



msTOEY. 27 

to the length of the string we use, — the longer the 
strmg, the nearer a circle will the figure become. 
This figure is the ellipse. The two points F F are 
called the/oa (singular, /ocz^s). We can now under- 
stand Kepler's attempt, and the glorious triumph 
which crowned his seventeen years of unflagging toil. 

First Laiv. — With this figure he constructed an 
orbit, haying the sun at the centre, and again fol- 
lowed the planet Mars in its course. But very soon 
there was as great discrepancy between the observed 
and computed places as before. Undismayed by 
this failure, Kepler assumed another hypothesis. 
He determined to place the sun at one of the foci 
of the elhpse, and once more "hunted down" the 
theory. For a whole year he traced the planet 
along the imaginary orbit, and it did not diverge. 
The truth was discovered at last, and Kepler an- 
nounced his first great law — 

Planets revolve in ellipses, with the sun at 
one focus. 

Second Law, — Kepler knew that the planets do 
not move with equal velocity in the different parts 
of their orbits. He next set about estabhsh- 
ing some law by which this speed could be deter- 
mined, and the place of the planet computed. He 
drew an ellipse, and marked the various positions of 
the planet Mars once more. He soon found that 
when at its 'perihelion (point nearest the sun) it 
moves the fastest, but when at its aphelion (point 
furthest from the sun) it moves the slowest. Once 



28 INTKODUCTION. 

more lie " hunted down" various hypotheses, until 
at last he discovered that while in going from B to 
A the planet moves very slowly, and from D to 

Fig. 3. 




very rapidly; yet the space inclosed between the 
lines SB and SA is equal to that inclosed between 
S D and S C. Hence the second law — 

A LINE CONNECTING THE CENTRE OF THE EABTH WITH 
THE CENTRE OF THE SUN, PASSES OVER EQUAL SPACES IN 
EQUAL TIMES. 

Third Laiu, — Kepler, not satisfied with the dis- 
covery of these laws, now determined to ascertain 
if there were not some relation existing between the 
times of the revolution of the planets about the sun 
and their distances from that body. With the same 
wonderful patience, he took the figures of Tycho 
Brahe, and began to compare them. He tried them 
in every imaginable relation. Next he took their 
squares, then he attempted their cubes, and lastly 
he combined the squares and the cubes. Here was 
the secret ; but he toiled around it, made a blunder, 



HISTORY. 29 

and waited for montlis, until, once more, his patience 
fcriumplied, and lie readied the third law — 

The squares of the times of revolution of the 
planets about the sun, are proportional to the 
cubes of their mean distances from the sun.* 

In rapture over the discovery of these three laws, 
so marked by that divine simpHcity which pervades 
all the laws of nature, Kepler exclaimed, " Nothing 
holds me. The die is cast. The book is written, to 
be read now or by posterity, I care not which. It 
may well wait a century for a reader, since God has 
waited six thousand years for an observer."t 

Galileo. — Contemporary with Kepler was the great 
Florentine philosopher, Galileo. He discovered the 
laws of the pendulum and of falling bodies, as we 
have already learned in Natural Philosophy. He, 
however, was educated in and believed the Ptolemaic 
theory. A disciple of the Copernican theory hap- 
pening to come to Pisa, where Galileo was teaching 



* For example : The square of Jupiter's period is to the square 
of Mars' period, as tlie cube of Jupiter's distance is to the cube 
of Mars' distance ; or, representing tlie earth's time of revolu- 
tion by P, and her distance from the sun by p, then letting D and 
d represent the same in another planet, we have the proportion 
P^ D' : : p^ d\ 

f Kepler, strangely enough, believed in the " Music of the 
Spheres." He made Saturn and Jupiter take the bass. Mars the 
tenor. Earth and Venus the counter, and Mercury the treble. 
This shows what a streak of folly or superstition may run 
through the character of the noblest man. However, as John- 
son says, a mass of metal may be gold, though there be in it a 
little vein of tin. 



30 INTEODUCTION. 

as professor in the University, drew his attention to 
its simplicity and beauty. His clear discriminating 
mind perceived its perfection, and he henceforth 
advocated it with all the ardor of his unconquerable 
zeal. Soon after he learned that one Jansen, a Dutch 
watchmaker, had invented a contrivance for making 
distant objects appear near. With his profound 
knowledge of optics and philosophical instruments, 
Galileo instantly caught the idea, and soon had a 
telescope completed that would magnify thirty times. 
It was a very simple affair — only a piece of lead 
pipe with glasses set at each end ; but it was the 
first telescope ever made, and destined to over- 
throw the old Ptolemaic theory, and revolutionize 
the whole science of Astronomy. 

Discoveries made with the telescojoe. — Gahleo now 
examined the moon. He saw its mountains and val- 
leys, and watched the dense shadows sweep over its 
plains. On January 8, 1610, he turned the telescope 
toward Jupiter. Near it he saw three bright stars, 
as he considered them, which were invisible to the 
naked eye. The next night he noticed that those" 
stars had changed their relative positions. Aston- 
ished and perplexed, he waited three days for a fair 
night in which to resume his observations. The 
fourth night was favorable, and he again found 
the three stars had shifted. Night after night he 
watched them, discovered a fourth star, and finally 
found that they were all rapidly revolving around 
Jupiter, each in its elliptical orbit, with its own rate 



mSTOEY. 31 

of motion, and all accompanying the planet in its 
journey around the sun. Here was a miniature 
Copernican system, hung up in the sky for all to see 
and examine for themselves. 

Becejotion of the discoveries. — Galileo met with the 
most bitter opposition. Many refused to look through 
the telescope lest they might become victims of the 
philosopher's magic. Some prated of the wickedness 
of digging out valleys in the fair face of the moon. 
Others doggedly clung to the theory they had held 
from their youth up. As a specimen of the arguments 
adduced against the new system, the following by 
Sizzi is a fair instance. " There are seven windows 
in the head, through which the air is admitted to the 
body, to enlighten, to warm, and to nourish it, — two 
nostrils, two eyes, two ears, and one mouth. So hi 
the heavens there are two favorable stars, Jupiter and 
Yenus ; two unpropitious. Mars and Saturn ; two 
luminaries, the Sun and Moon ; and Mercury alone, 
undecided and indifferent. From which, and from 
many other phenomena of Nature, such as the seven 
metals, etc., we gather that the number of planets is 
necessarily seven. Moreover, the satellites are in- 
visible to the naked eye, can exercise no influence 
over the earth, and would be useless, and therefore 
do not exist. Besides, the week is divided into seven 
days, which are named from the seven planets. Now, 
if we increase the number of planets, this whole 
system falls to the ground." 

Newton. — As we have seen, the truth of the Co- 



32 INTRODUCTION. 

pernican system was fully established by the discov- 
eries of Galileo with his telescope. Philosophers 
gradually adopted this view, and the Ptoleraaic 
theory became a relic of the past. In 1666, Newton, 
a young man of twenty-four years, was spending a 
season in the country, on account of the plague 
which prevailed at Cambridge, his place of resi- 
dence. One day, while sitting in a garden, an apple 
chanced to fall to the ground near him. Reflecting 
upon the strange power that causes all bodies thus 
to descend to the earth, and remembering that this 
force continues, even when we ascend to the tops of 
high mountains, the thought occurred to his mind, 
" May' not this same force extend to a great distance 
out in space ? Does it not reach the moon ?" 

Laivs of Motion. — To understand the philosophy 
of the reasoning that now occupied the mind of 
Newton, let us apply the laws of motion as we have 
learned them in Philosophy. When a body is once 
set in motion, it will continue to move forever in a 
straight line, unless another force is applied. As 
there is no friction in space, the planets do not lose 
any of their original velocity, but move now with the 
same speed which they received in the beginning 
from the Divine hand. But this would make them 
all pass through straight, and not circular orbits. 
"Wliat causes the curve? Obviously another force. 
For example : I throw a stone into the air. It 
moves not in a straight line, but in a curve, because 
the earth constantly bends it downward. 



HISTOEY. 36 

Application. — Just so tlie moon is moving around 
the earth, not in a straight line, but in a curve. Can 
it not be that the earth bends it downward, just as 
it does the stone ? Newton knew that a stone falls 
toward the earth sixteen feet the first second. He 
imagined, after a careful study of Kepler's laws, 
that the attraction of the earth diminishes according 
to the square of the distance. He knew (according 
to hhe measurement then received) that a body on 
the surface of the earth is four thousand miles from 
the centre. He applied this imaginary law. Sup- 
ipoiH it is removed four thousand miles from the 
surface of the earth, or eight thousand miles from 
the centre. Then, as it is twice as far from the 
centre, its weight will be diminished 2^, or 4 times. 
If it were placed 3, 4, 5, 10 times further away, its 
weight would then decrease 9, 16, 25, 100 times. 
If, then, the stone at the surface of the earth (four 
thousand miles from the centre) falls sixteen feet 
the first second, at eight thousand miles it would 
fall only four feet ; at 240,000 miles, or the distance 
of the moon, it would fall only about one-twentieth 
of an inch (exactly .053). Now the question arose, 
" How far does the moon fall toward the earth, i. e., 
bend from a straight line, every second ?" For sev- 
enteen years, with a patience rivalling Kepler's, this 
philosopher toiled over interminable columns of fig- 
ures to find how much the moon's path around the 
earth curves each second. He reached the result 
at last. It was nearly, but not quite exact. ^ Disap- 



34 INTRODUCTION. 

pointed, lie laid aside his calculations. Kepeatedly 
lie reviewed them, but could not find a mistake. At 
length, while in London, he learned of a new and 
more accurate measurement of the distance fi^om the 
circumference to the centre of the earth. He has- 
tened home, inserted this new value in his calcula- 
tions, and soon found that the result would be cor- 
rect. Overpowered by the thought of the gTand 
truth just before him, his hand faltered, and he 
called upon a friend to complete the computation. 

From the moon, Newton passed on to the other 
heavenly bodies, calculating and testing their orbits. 
At last he turned his attention to the sun, and, by 
reasoning equally conclusive, proved that the attrac- 
tion of that great central orb compels all the planets 
to revolve about it in elliptical orbits, and holds 
them with an irresistible power in their appointed 
paths. At last he announced this grand Law of 
Gravitation : 

Every particle of matter in the universe at- 
tracts EVERY OTHER PARTICLE OF MATTER WITH A 
FORCE DIRECTLY PROPORTIONAL TO ITS QUANTITY OF 
MATTER, AND DECREASING AS THE SQUARE OF THE DIS- 
TANCE INCREASES. 



SPACE. 35 



SPACE. 



We now in imagination pass into space, wliich 
stretclies out in every direction without bounds or 
measures. We look up to the heavens and try to 
locate some object among the mazes of the stars. 
We are bewildered, and immediately feel the neces- 
sity of some system of measurement. Let us try to 
understand the one adopted by astronomers. 

The Celestial Sphere. — The blue arch of the sky, 
as it appears to be spread above us, is termed the 
Celestial Sphere. There are two points to be no- 
ticed here. First, that so far distant is this imagi- 
nary arch from us, that if any two parallel lines from 
different parts of the earth are drawn to* this sphere, 
they will apparently intersect. Of course this can- 
not be the fact ; but the distance is so immense, that 
we are unable to distinguish the httle difference of 
four or even eight thousand miles, and the two lines 
will seem to unite : so we must consider this great 
earth as a mere speck or point at the centre of the 
Celestial Sphere. Second, that we must even neg- 
lect the entire diameter of the earth's orbit, so that 
if we should draw two parallel lines, one from each 
end of the earth's orbit, to the sphere, although 
these Hues would be 183,000,000 miles apart, yet 
they would be extended so far that we could not 
separate them, and they would appear to pierce the 
sphere at the same point ; which is to say, that at 



36 INTRODUCTION. 

that enormous distance, 183,000,000 miles shrink to 
a point. Consequently, in all parts of the earth, and 
in every part of the earth's orbit, we see the fixed 
stars in the same place. This sphere of stars sur- 
rounds the earth on every side. In the daytime we 
cannot see the stars because of the superior light of 
the sun ; but with a telescope they can be traced, 
and a skiKul astronomer will find a star as well at 
noon as at midnight. Indeed, when looking at the 
sky from the bottom of a deep well or lofty chimney, 
if a bright star happens to be directly overhead, it 
can be seen with the naked eye even at midday. In 
ihis way it is said a celebrated optician was first led 
fco think of there being stars by day as well as by 
night. One half of the sphere is constantly visible 
to us ; and so far distant are the stars, that we see 
just af much of the sphere as we would if the upper 
part of the earth were removed, and we were to 
stand four thousand miles further away, or at the 
very centre of the earth, where our view would be 
bounded by a great circle of the earth. On the con- 
cave surface of the celestial sphere there are imag- 
ined to be drawn three systems of circles : the HoEi- 
zoN, the Equinoctial, and the Ecliptic Systems. 
Each of these has (1) its Principal Circle, (2) its 
Subordinate Circles, (3) its Points, and (4) its Meas^ 
urements. 



SPACE. 37 

I. The Hokizon System. 

(a) The Principal Circle is the Rational Horizon. 
This is the great circle that, passing through the 
centre of the earth, separates the visible from the 
invisible heavens. The Sensible Horizon is the small 
circle where the earth and sky seem to meet ; it is 
parallel to the rational horizon, but distant from it 
the semi-diameter of the earth. No two places have 
the same sensible horizon : any two on opposite 
sides of the earth have the same rational horizon. 

ih) The Subordinate Circles. — These are the 
Prime Vey^tical circle and the Meridian. A vertical 
circle is one passing through the poles of the horizon 
(the zenith and nadir). The Prime Yertical is a 
vertical circle passing through the East and West 
points. The Meridian is a vertical circle passing 
through the North and South points. 

(c) Points. — These are the Zenith, the Nadir, the 
K, S., E., and W. points. The Zenith is the point 
directly overhead, and the Nadir the one directly 
underfoot. They are also the poles of the horizon 
— i. e., the jjoints where the axis of the horizon 
pierces the celestial sphere. The N., S., E., and W. 
points are familiar to all. 

(d) Measurements. — These are Azimuth, Ampli- 
tude, Altitude, and Zenith distance. 

Azimuth is the distance from the meridian, meas- 
ured East or West, on the horizon (to a vertical 
circle passing through the object). 



38 INTBODUCTION. 

Amplitude (tlie complement of Azimutli) is the 
distance from tlie Prime Vertical, measured on tlie 
horizon, North or South. 

Altitude is the distance from the horizon, meas- 
ured on a vertical circle toward the zenith. 

Zenith distance (the complement of Altitude) is the 
distance from the zenith, measured on a vertical 
circle, toward the horizon. 

The Horizon System is the one commonly used 
in observations with Mural Circles and Transit In- 
struments. 



n. The Equinoctlil System. 

(a) The Pkincipal Circle is the Equinoctial. This 
is the Celestial Equator, or the earth's equator, ex- 
tended to the Celestial Sphere. 

ih) Suboedinate Circles. — These are the Hour 
Circles (Right Ascension Meridians) and the Decli- 
nation Parallels. The Hour Circles are thus lo- 
cated. The Equinoctial is divided into 360°, equal 
to twenty-four hours of motion — thus making 15° 
equal to one hour of motion. Through these divi- 
sions run twenty-four meridians, each constituting 
an hour of motion (time) or 15° of space. The 
Hoar Circles may be conceived as meridians of ter- 
restrial longitude (15° apart) extended to the Celes- 
tial Sphere. (See Colures, p. 40.) 

The Declination Parallels are small circles par- 
allel to the Equinoctial ; or they may be conceived 



SPACE. 39 

as the parallels of terrestrial latitude extended to 
the Celestial Sphere. 

(c) The Points are the Celestial Poles and the 
Equinoxes. The Celestial Poles are the points where 
the axis of the earth extended pierces the Celestial 
Sphere, and are the extremities of the celestial axis, 
just as the poles of the earth are the extremities of 
the earth's axis. The North Point is marked very 
nearly by the North Star, and every direction from 
that is reckoned South, and every direction toivard 
that is reckoned North, however it may conflict with 
our ideas of the points of the compass. 

The Equinoxes are the points where the Equi- 
noctial and the Ecliptic (the sun's apparent path 
through the heavens) intersect. 

{d) The Measukements are Bight Ascension (E. A.), 
Declination^ and Polar Distance. 

Right Ascension is distance from the Vernal Equi- 
nox, measured on the equinoctial eastward. E. A. 
corresponds to terrestrial longitude, and may ex- 
tend to 360° East, instead of 180° as on the earth. 
E. A. is never measured westward. The starting 
point is the meridian passing through the vernal 
equinox; as the meridian passing through Green- 
wich is the point from which terrestrial longitude 
is measured. 

Declination is distance from the equinoctial, meas- 
ured on any vertical circle or meridian North or 
South. It corresponds to terrestrial latitude. 

Polar distance (the complement of Declination) is 



40 INTRODUCTION. 

the distance from the Pole, measTired on a vertical 
circle. 

The Equinoctial System is largely used by modern 
astronomers, and accompanies the Equatorial Tele- 
scope, Sidereal Clock, and Chronographs of the best 
Observatories. 



III. The Ecliptic System. 

(a) The Principal Circle is the Ecliptic. This is 
the earth's orbit about the sun, or the apparent 
path of the sun in the heavens. It is inclined to 
the equinoctial 23° 28', which measures the inclina- 
tion of the axis of the earth to its orbit, and is called 
the obliquity of the ecliptic. 

(h) The Secondary Circles are Circles of Celestial 
Longitude, the Colures, and Parallels of Celestial 
Latitude. 

The Circles of Celestial Longitude are now less 
employed. They are measured on the Ecliptic, as 
circles of Right Ascension (R. A.) are now measured 
on the Equinoctial. 

The Colures are two principal meridians ; the 
Equinoctial Colure is the meridian passing through 
the equinoxes ; the Solstitial Colure is the meridian 
passing through the solstitial points. 

The Parallels of Celestial Latitude are now little 
used, but are small circles drawn parallel to the 
ecliptic, as parallels of declination are now drawn 
parallel to the equinoctial. 



SPACE. 41 

(c) The Points are the Poles of the Ecliptic, the 
Uquinoxes, and the Solstitial Points. 

The Poles of the Ecliptic are the points where the 
axis of the earth's orbit meets the Celestial Sphere. 
(Little used.) 

The Equinoxes are the points where the ecliptic 
intersects the equinoctial. The place where the 
sun crosses the equinoctial* in going North, which 
occurs about the 21st of March, is called the Yernal 
Equinox. The place where the sun crosses the 
equinoctial in going South, which occurs about the 
21st of September, is called the Autumnal Equinox. 
The Solstices are the two points of the ecliptic most 
distant from the Equator; or they may be con- 
sidered to mark the sun's furthest declination. North 
and South of the equinoctial. The Summer Sol- 
stice occurs about the 22d of June ; the Winter Sol- 
stice occurs about the 22d of December. 

(d) The Measukements are celestial longitude and 
latitude. 

Celestial longitude is distance from the Yernal Equi* 
nox measured on the ecliptic, eastward. 

Celestial latitude is distance /rom the ecliptic meas- 
ured on a Secondary circle. 

The Zodiac. 

A belt of the Celestial Sphere, 9° on each side of 
the ecliptic, is styled the Zodiac. This is of very 



* This is wliat is commonly called " crossing the line. 



42 INTEODUCTION. 

high antiquity, having been in use among th€ an- 
cient Hindoos and Egyptians. The Zodiac is di- 
vided into twelve equal parts — of 30° each — called 
Signs, to each of which a fanciful name is given. 
The following are the names of the 



Signs of the Zodiac, 
Libra . , . 



Aries t 

Taurus « 

Gemini n 

Cancer © 

Leo ^ 

Yirgo ,' . m 



........ =2: 

Scorpio TTL 

Sagittarius f 

Capricornus ...... \5 

Aquarius ^ 

Pisces ^ 



"The first, t, indicates the horns of the Kam ; 
the second, « , the head and horns of the Bull ; the 
barb attached to a sort of letter m, designates the 
Scorpion ; the arrow, t , sufficiently points to Sagit- 
tarius ; v3 is formed from the Greek letters rp, the 
two first letters of rp'iyoc, a goat Finally, a bal- 
ance, the flowing of water, and two fishes, tied by 
a string, may be imagined in ^, ^^, and k, the signs 
of Libra, Aquarius, and Pisces." 



^ju mlm M^tm. 



In them hath He set a tabernacle for the sun." 

Psalm xix 4. 



THE SOLAR SYSTEM. 



The Solar System is comprised within the limits 
of the Zodiac. It consists of — 

1. The Sun — the centre. 

2. The major planets — Yulcan (undetermined), Mercury 

Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. 
3 The minor planets, at present one hundred and one in 
number. 

4. The satellites or moons, eighteen in number (the pathh 

of some extend outside the Zodiac), which revolve 
around the different planets. 

5. Meteors and shooting-stars. 

6. Nine comets whose orbits have been computed, and 

over two hundi^ed of which little is known. 

7. The Zodiacal Light. 

How WE AKE TO IMAGINE THE SOLAR SYSTEM TO OUR- 
SELVES. — We are to think of it as suspended in 
space ; being held up, not by any visible object, but 
in accordance with the law of Universal Gravitation 
discovered by Newton, whereby each planet attract? 
every other planet and is in turn attracted by alL 
First, the Sun, a great central globe, so vast as 
to overcome the attraction of all the planets, and 
compel them to circle around him ; next, the planets, 
each turning on its axis while it flies around the 



4:6 THE SOLAR SYSTEM. 

siin in an elliptical orbit ; then, accompanying these, 
the satellites, each revolving about its own planet, 
while all whirl in a dizzy waltz about the central 
orb ; next, the comets, rushing across the planetary 
orbits at irregular intervals of time and space ; and 
finally, shooting-stars and meteors darting hither 
and thither, ifiterweaving all in apparently inextri- 
cable confusion. To make the picture more wonder- 
ful still, every member is flying with an inconceiv- 
able velocity, and yet with such accuracy that the 
solar system is the most perfect timepiece known. 



THE SUN. 

Sign, 0, a buckler with its boss. 

Distance. — The sun's average distance from the 
earth is about 91J million miles. Since the orbit of 
the earth is elliptical, and the sun is situated at one 
of its foci, the earth is nearly 3,000,000 miles further 
from the sun in aphehon than in perilielion. As we 
attempt to locate the heavenly bodies in space, we 
are immediately startled by the enormous figures 
employed. The first number, 91,500,000 miles, is 
far beyond our gxasp. Let us try to comprehend it. 
If there were air to convey a sound from the sun to 
the earth, and a noise could be made loud enough to 
pass that distance, it would require over fourteen 
years for it to come to us. Suppose a railroad 



THE SUN. 47 

could be built to the sun. An express-train, travel- 
ling day and night, at the rate of thirty miles an 
hour, would require 341 years to reach its desti- 
nation. Ten generations would be born and would 
die ; the young men would become gray-haired, and 
their great-grandchildren would forget the story of 
the beginning of that wonderful journey, and could 
find it only in history, as we now read of Queen 
Elizabeth or of Shakspeare ; the eleventh generation 
would see the solar depot at the end of the route. 
Yet this enormous distance of 91,500,000 miles is 
used as the unit for expressing celestial distances 
— as the foot-rule for measuring space ; and astron- 
omers speak of so many times the sun's distance 
as we speak of so many feet or inches. 

The Light of the Sun. — This is equal to 5,563 
wax-candles held at a distance of one foot from the 
eye. It would require 800,000 full-moons to pro- 
duce a day as brilliant as one of cloudless sunshine. 

The Heat of the Sun. — The amount of heat we 
receive annually is sufficient to melt a layer of ice 
thirty-eight yards in thickness, extending over the 
whole earth. Yet the sunbeam is only ttoIo-oo- P^i'* 
as intense as it is at the surface of the sun. More- 
over, the heat and light stream off into space equally 
in every direction. Of this vast flood only one 
twenty-three hundred millionth part reaches the 
earth. It is said that if the heat of the sun were 
produced by the burning of coal, it would require a 
layer ten feet in thiclmess, extending over the whole 



48 THE SOLAR SYSTEM. 

sun, to feed the flame a single hour. Were the sun 
a solid body of coal, it would burn up at this rate in 
foriy-six centuries. Sir John Herschel says that if 
a solid cylinder of ice 45 miles in diameter and 
200,000 miles long were plunged, end first, into the 
sun, it would melt in a second of time. 

Apparent size. — It appears to be about a haK de- 
gree in diameter, so that 360 disks like the sun, laid 
side by side, would make a haK circle of the celestial 
sphere. It seems a little larger to us in winter than 
in summer, as we are 3,000,000 miles nearer it. If 
we represent the luminous surface of the sun when 
at its average (mean) distance by 1000, the same sur- 
face will be represented to us when in aphelion (July) 
by 940, and when in perihelion (January) by 1072. 

Dimensions. — Its diameter is about 850,000 miles.^ 
Let us try to understand this amount by comparison. 

A mountain upon the surface of the sun, to bear 
the same proportion to the globe itself as the Dha- 
walaghiri of the Himalayas does to the earth, would 
have to be about six hundred miles high. 

Again : Suppose the sun were hollow, and the 
earth, as in the cut (Fig. 4), placed at the centre, not 
only would there be room for the moon to revolve 
in its regular orbit within the shell, but that would 
stretch off in every direction 200,000 miles beyond. 

Its volume is 1,245,000 times that of the earth — 

* Pythagoras, whose theory of the universe was in so many 
respects very like the one we receive, believed the sun to be 
44,000 miles from the earth, and 75 miles in a>'^'^'^ter. 



THE SUN. 



49 



I. e., it would take 1,245,000 earths to make a globe 
the size of the sun. Its mass is 674 times that of 
all the rest of the solar system. Its iveight may be 
expressed in tons thus, 

1 , 910 , 278 , 070 , 000 , 000 , 000 , 000 , 000 , 000, 

Fig. 4. 




a number which is meaningless to our imagination, 
but yet represents a force of attraction which holds 
our own earth and all the planets steadily in then* 
places ; while it fills the mind with an indescribable 
awe as we think of that Being who made the sun, 
and holds it in the very palm of his hand. 



50 THE SOLAR SYSTEM. 

The density of the sun is only about one-fourth 
that of the earth, or 1.43 that of water, so that 
the weight of a body transferred from the earth to 
the sun would not be increased in proportion to the 
comparative size of the two. On account also of 
the vast size of the sun, its surface is so far from 
its centre that the attraction is largely diminished, 
since that decreases, we remember, as the square of 
the distance. However, a man weighing at the 
earth's equator 150 lbs., at the sun's equator would 
weigh about 4,080 lbs., — a force of attraction that 
would inevitably and instantly crush him. At the 
earth's equator a stone falls 16 feet the first second ; 
at the sun's equator it would fall 437 feet. 

Telescopic Appearance of the Sun : Sun-spots. — 
We may easily examine the sun at early morning or 
late at evening with the naked eye, and even at mid- 
day by using a smoked glass. The disk wiU appear 
to us perfectly distinct and circular, and with no 
spot to dim its brightness. If we use, however, a 
telescope of moderate power, taking the precaution 
to properly shield the eye with a colored eye-piece, 
we shall find its surface sprinkled with irregular spots, 
somewhat as shown in the accompanying figure. 

Curious opinions concerning solar spots. — The nat- 
ural purity of the sun seems to have been formerly 
an article of faith among astronomers, and therefore 
on no account to be called in question. Scheiner, 
it is said, having reported to his superior that he 
had seen spots on the sun's face, Avas abruptly dis- 



THE SUN. 51 

missed with these remarks : " I have read Aristotle's 
writings from end to end many times, and I assure 
you I do not find anything in them similar to that 
which you mention. Go, my son, tranquillize your- 
self ; be assured that what you take for spots are 
the faults of your glasses or your own eyes." 



Fig. 5 




8UN IN TELESCOPE. 



Discovery of the solar spots. — They seem to have 
been noticed as early as 807 A. d., although the tel- 
escope was not invented until 1610, and Galileo dis- 
covered the solar spots in the following year. We 



52 THE SOLAE SYSTEM. 

read in the log-book of the good ship Eichard of 
Arundell, on a voyage, in 1590, to the coast of 
Guinea, that " on the 7, at the going downe of the 
snnne, we saw a great black spot in the sunne ; and 
the 8 day, both at rising and setting, we saw the 
like, — which spot to me seeming was about the big- 
nesse of a shilling, being in 5 degrees of latitude, 
and still there came a great billow out of the souther 
board." 

Number and location of spots. — Sometimes, but 
rarely, the disk is clear. During a period of ten 
years, observations were made on 1982 days, on 372 
of which there were no spots seen. As many as 
two hundred spots have been noticed at one time. 
They are mostly found in two belts on each side of 
the equator, within not less than 8° nor more than 
35° of latitude. They seem to herd together — the 
length of the stragghng group being generally par- 
allel to the equator. 

The size of the spots. — It is not uncommon to find 
a spot with a surface larger than that of the earth. 
Schroter measured one more than 29,000 miles in 
diameter. Sir J. W. Herschel calculated that one 
which he saw was 50,000 miles in diameter. In 
1843 one was seen which was 14,816 miles across, 
and was visible to the naked eye for an entire 
week. On the day of the eclipse in 1858, a spot 
over 107,000 miles broad was distinctly seen, and 
attracted general attention in this country. Some 
who read this paragraph wiU doubtless recall its ap^ 



THE SUN. 



53 



Fig. 6. 



pearance. In 1839, Captain Davis saw one which 
he computed was not less than 186,000 miles long, 
and had an area of twenty-five billion square miles. 
If these are deep openings in the luminous atmos- 
phere of the sun, what an abyss must that be at 
"the bottom of which our earth could lie Like a 
boulder in the crater of a volcano !" 

The spots consist of distinct parts. — From the ac- 
companying representation it will be seen that the 
spots generally consist of one or more dark portions 
called the umbrae and around that a grayish portion 
styled the pe- 
numbra (pene, 
almost, and um- 
hra^ black). — 
Sometimes, how- 
ever, umbrae ap- 
pear without a 
penumbra, and 
vice versa. The 
umbra itself has 
generally a 
dense black 
centre, cftUed the 
nucleus. Besides 
this, the umbra is Sometimes divided by luminous 
bridges. 

The spots are in motion. — They change from day 
to day ; but they all have a common movement. 
About fourteen days are required for a spot to pass 




SUN SPOTS. 



54 THE SOLAR SYSTEM. 

across the disk of the sun from the eastern side or 
lirrib to the western ; in fourteen days it reappears, 
changed in form perhaps, but generally recognizable. 
The spots change their rapidity and apparent form 
as they pass across the dish. — A spot is seen on the 
eastern limb ; day by day it progresses, with a grad- 
ually increasing rapidity, until it reaches the cen- 




CHANGE IN SPOTS AS THEY CROSS THE DISK, 

tre ; it now gradually loses its rapidity, and finally 
disappears on the western limb. The diagram il- 
lustrates the apparent change which takes place in 
the form. Suppose at first it is of an oval shape : 
as it approaches the centre it apparently widens 
and becomes circular. Having passed that point, 
it becomes more and more oval until it disappears. 

This change in the spots proves the sun's rotatiov 
on its axis. — These changes can be accounted for 
only on the supposition that the sun revolves on its 
axis : indeed, ttiey are the precise effects which the 



THE SUN. 



65 



laws of perspective demand in that case. About 
twenty-seven days (27 d., 7 h.) elapse from the ap- 
pearance of a spot on the eastern limb before it 
reappears a second time. During this time the 
earth has gone forward in its orbit, so that the 
location of the observer is changed ; allowing for 
this, the sun's time of rotation is about twenty- 
five days (25 d., 8 h., 10 m. : Langier.) 




STNODIC AND SIDEREAL REVOLUTION. 



Synodic and sidereal revolution of tlie s'pots. — We 
can easily understand why we make an allowance 
for the motion of the earth in its orbit. Suppose a 



56 THE SOLAK SYSTEM. 

solar spot at a, on a line passing from the centre of 
the earth to the centre of the sun. For the spot to 
pass around the sun and come into that same posi- 
tion again, requires about twenty-seven days. But 
during this time, the earth has passed on from T to 
T'. The spot has not only travelled around to a 
again, but also beyond that to a', or the distance 
from a to a' more than an entire revolution. To do 
this requires, as we have said, about two days. A 
revolution from a around to a' again is called a 
synodic, and one from a around to a again is called 
a sidereal revolution. 

The spots apparently do not always move in 
straight lines. — Sometimes their path curves toward 

MARCH. JUKE. SEPTIEMBEK. 






the north, and sometimes toward the south, as in 
the figure. This can be explained only on the sup- 
position that the sun's axis is inclined to the 
ecliptic (7° 15'). 

The spots have a motion of their own. — Besides the 
motion already named as assigned to the sun's rota- 
tion, the spots seem to have a motion of their own, 



THE SUN. 57 

and this fact is undoubtedly the cause of the va- 
riation in the estimates made of the time of the 
sun's revolution on its axis. A spot on the equator 

. Fig. 10. 




performs a synodic revolution in about twenty-five 
days, while one half way to either pole requires 
twenty-eight days. One spot was noticed which 
had a motion three times greater than that of clouds 
driven along by the most violent hurricane. Again, 
immense cyclones occasionally pass over the surface 
with fearful rapidity, producing rotation and sudden 
changes in the spots. At other times, however, the 
spots seem " to set sail and move across the disk of 
the sun like gondolas over a silver sea." 

The spots change their real foriin. — Spots break out 
and then disappear under the very eye of the astron- 
omer. WoUaston saw one that seemed to be shat- 



58 THE SOLAE SYSTEM. 

tered Ijke a fragment of ice when it is thrown on a 
frozen surface, breaking into pieces, and shding off 
in every direction. Sometimes one divides itseK 
into several nuclei, while again several nuclei com- 
bine into one. Occasionally a spot will remain for 
six or eight rotations, while often one will last 
only half an hour. In one case. Sir. W. Herschel 
relates that when examining a spot through his 
telescope, he turned away for a moment, and on 
looking back it was gone. 

The appearance of the spots is periodical. — It is a 
remarkable fact that the interval between the great- 
est and least number of spots is about 11.11 years. 
These variations seem also to be connected with 
periodical variations in the aurora, and magnetic 
H-arth-currents which interfere with the telegraph. 
The regular increase and diminution in the spots 
was discovered by Schwabe of Prussia, who watched 
the sun so carefully that it is said, " for thirty years 
the sun never appeared above the horizon without 
being confronted by his imperturbable telescope." 
Besides this, it has now been found that the activit}^ 
of the sun's spots goes through another regular 
period of about 56 years. Independently of this 
conclusion, it has also been discovered that the 
aurora has a similar period of 56 years. 

The spots are influenced by the planets. — They ap- 
pear to be especially sensitive to the approach of 
Yenus, on account of its nearness, and of Jupiter, 
because of its size. The area of the spots exposed 



THE SUN. 59 

to view from the earth is uniformly greatest when 
Yenus is on the opposite side of the sun from us, 
and least when on the same side. When both 
Venus and Jupiter are on the side of the sun op- 
posite to us, the spots are much larger than when 
Venus alone is in that position. In part explana- 
tion of this influence of the planets, we may suppose 
that they withdraw heat or modify reflection on the 
disk of the sun exposed to their action, and thus 
cause a condensation of gases. 

The spots do not influence the fruitfulness of the sea- 
son. — Sir W. Herschel first advanced the idea that 
years of abundant spots would be years also of plen- 
tiful harvest. This is not now generally received. 
What two years could be more dissimilar than 1859 
and 1860 ? Both abounded in solar spots, yet one 
was a fruitful year and the other almost one of 
famine in Europe. 

The spots are cooler than the surrounding surface. — 
It seems that the breaking out of a spot sensibly 
diminishes the temperature of that portion of the 
sun's disk. The faculae, on the other hand, do no'' 
increase the temperature. (Secchi.) 

The spots are depressions below the luminous surf at , 
— This was thought probable before, but is concj 
sively proved by the photographs of the sun, which 
have been taken in large numbers of late at Kew 
Observatory. 

Comparative brightness of spots and sun. — If we 
represent the ordinary brightness of the sun by 



60 



THE SOLAE SYSTEM. 



Fig. 11. 



1,000, then that of the penumbra would be 469, and 
that of the nucleus 7. There may be much light 
and heat radiated by a spot, which seems totally 
black as compared with the sun : we remember that 
when we look through even a Drummond light at 
the sun, it appears as a black spot on the disk of 
that luminary. 

Facul(E, luillow-lea/f and mottled appearance. — Be- 
sides the variety of 
spots already de- 
scribed, there are 
other curious ap- 
pearances worthy of 
note. Bright ridges 
or streaks appear, 
which constitute the 
most brilliant por- 
tions of the sun. — 
These are called fa- 
cuke. They vary 
from barely discem- 
^^^^^- ible, softly-gleaming 

tracts 1,000 miles long, to lofty, piled-up, mountain- 
ous regions 40,000 miles long and 4,000 broad. Out- 
side of the spots, the entire disk of the sun is covered 
with minute shady dots, giving it a mottled appear- 
ance not unUke that of the skin of an orange, though 
less coarse. Under a large telescope the surface seems 
to be entirely made up of luminous masses, imperfectly 
separated by dark dots called pores. These masses are 




THE SUN. 



61 



said by Mr. Nasmyth to have a "willow-leaf" shape; 
many observers apply other descriptive terms, such 
as " rice grains," " untidy circular masses," " things 
twice as long as broad," " granules," etc. The ac- 
companying cut represents the willow-leafed struc- 
ture of the luminous surface, and also the " bridges" 



Pig 12. 




1*1 






m-mmmm * 










WLLLOW-LEAF. 



spanning the solar spot. Indeed, it is said that 
the spots themselves always have their origin in a 
"pore," which appears to slowly increase and as- 
sume the blackness of an umbra, after which the 
penumbra begins to appear. 
Physical Constitution of the Sun. — Of the consti- 



62 THE SOLAE SYSTEM. 

tution of the sun, and consequent cause of the 
solar spots, very little is definitely known. We shall 
notice the various theories now adopted by different 
astronomers. 

Wilson's Theoey. — This theory supposes that the 
sun is composed of a solid, dark globe, surrounded 
by three atmospheres. The first, nearest the black 
body of the sun, is a dense, cloudy covering, pos- 
sessing high reflecting power. The second is called 
the photosphere. It consists of an incandescent gas, 
and is the seat of the hght and heat of the sun. 
The third, or outer one, is transparent, very like our 
atmosphere. According to this theory, the spots 
are to be explained in the following manner. They 
are simply openings in these atmospheres made by 
powerful upward currents. At the bottom of these 
chasms we see the dark sun as a nucleus at the 
centre, and around this the cloudy atmosphere — the 
penumbra. This explains a black spot with its 
penumbra. Sometimes the opening in the photo- 
sphere may be smaller than that in the inner or 
cloudy atmosphere ; in that case there will be a 
black spot without a penumbra. It will be natural 
to suppose that when the heated gas of the photo- 
sphere or second atmosphere is thus violently rent 
asunder by an eruption or current from below, 
luminous ridges will be formed on every side of 
the opening by the heaped-up gas. This will ac- 
count for the faculce surrounding the sun-spots. 
It will be natural, also, to suppose that sometimes 



THE SUN. 



63 



the cloudy atmosphere below will close up first over 
the dark surface of the sun, leaving only an open- 
ing through the photosphere, disclosing at the bot- 
tom a grayish surface of 'penumbra. We can readily 



F\z n 




WILSON'S THEORY. 



see, also, how, as the sun revolving on its axis brings 
a spot nearer and nearer to the centre, thus giving us 
a more direct view of the opening, we can see 
more and more of the dark body. Then as it passes 
by the centre the nucleus will disappear, until 
finally we can see only the side of the fissure, the 



64 THE SOLAE SYSTEM. 

penumbra, which, in its turn, will pass from oui 
sight. The existence of an outer atmosphere will 
account for the fact that the sun's margin is not so 
bright as its centre. 

Kjechhofp's Theory. — This view differs essentially 
from that of Wilson. It considers the sun as an 
intensely white-hot solid or fluid body surrounded 
by a dense atmosphere of flame, fiUed with sub- 
stances volatilized by the vivid heat. Changes of 
temperature take place, which give rise to tornadoes 
and violent tempests. Descending currents pro- 
duce openings filled with clouds, which appear as 
black spots on the sun's disk. A cloud once formed 
becomes a screen to shield the upper regions from 
the direct heat of the body of the sun. Thus a 
lighter cloud is produced, which gives the appear- 
ance of a penumbra around the spots. 

Spectrum analysis. — The hypothesis just given of 
the constitution of the sun rests upon the discov- 
eries of the spectroscope. This subject wiU be 
treated hereafter under the head of Celestial Chem- 
istry. Wilson's theory is time-honored, but compli- 
cated ; Kirchhoff's is modern, and partakes of the 
simplicity of true science. 

The Heat of the Sun. — This subject is not under- 
stood. Many theories have been advanced, but 
none has been generally adopted. Some have 
supposed the heat is produced by condensation, 
whereby the size of the sun is being constantly de- 
, creased. The dynamic theory accounts for the heat 



THE PLANETS. 65 

and the solar spots by assuming that there are vast 
numbers of meteors revolving around the sun, and 
that these constantly rain down upon the surface of 
that luminary. Their motion being stopped and 
changed to heat, feeds this great central fire. Were 
Mercury to strike the sun in this way, it would 
generate sufficient heat to compensate the loss by 
radiation for seven years. Many suppose that the 
heat of the sun is gradually diminishing. Of this 
we may be assured, there is enough to support life 
on our globe for millions of years yet to come. 



THE PLANETS. 



We shall describe these in regular order, passing 
outward from the sun. In this journey we shall ex- 
amine each planet in turn, noticing its distance, 
size, length of its year, duration of day and night, 
temperature of the climate, the number of its moons, 
and many other interesting facts, showing how much 
we can know of its world-life in spite of its wonder- 
ful distance. We shall encounter the earth in our 
imaginary wanderings through space, and shall ex- 
plain many celestial phenomena already partially 
familiar to us. In all these worlds we shall find 
traces of the same Divine hand, moulding and 
directing in conformity to one universal plan. The 
laws of light and heat will be invariable. The law 



66 THE SOLAE SYSTEM. 

of grayitation, wliicli causes a stone to fall to the 
ground, will be found to apply equally to the most 
distant planets. Even the very elements of which 
they are composed will be familiar to us, so that a 
book of natural science published here would, in all 
its general features, answer for use in a school on 
Mars or Jupiter. 

Characteristics common to the Planets. (Hind.) 
— 1. They move in the same invariable direction 
around the sun ; their course, as viewed from the 
north side of the ecliptic, being contrary to the 
motion of the hands of a watch. 

2. They describe oval or eUiptical paths round 
the sun — not, however, differing greatly from circles. 

3. Their orbits are more or less inclined to the 
ecliptic, and intersect it in two points, which are the 
nodes — one haK of the orbit lying north and the 
other south of the earth's path. 

4. They are opaque bodies like the earth, and 
shine by reflecting the light they receive from the 
sun. 

5. They revolve upon their axes in the same way 
as the earth. This we know by telescopic observa- 
tion to be the case with many planets, and by anal- 
ogy the rule may be extended to all. Hence they 
will have the alternation of day and night like the 
inhabitants of the earth ; but their days are of dif- 
ferent lengths from our own. 

6. Agreeably to the principles of gravitation, their 
velocity is greatest at those parts of their orbit 



THE PLANETS. 67 

which are nearest the sun, and least at the parts 
which are most distant from it ; in other words, 
they move quickest in perihehon, and slowest in 
aphelion. 

COMPAKISON OF THE TWO GrOUPS OF THE MaJOR 

Planets. (Chamhers.) — Separating the major plan- 
ets into two groups, if we take Mercury, Venus, the 
Earth, and Mars as belonging to the interior, and 
Jupiter, Saturn, Uranus, and Neptune to the exterior 
group, we shall find that they differ in the following 
respects : 

1. The interior planets, with the exception of the 
earth, are not, so far as we know, attended by any 
satellite, while the exterior planets all have satel- 
Htes. "We can but consider this as one of the 
many instances to be met with, in the universe, of 
the beneficence of the Creator, and that the satel- 
lites of these remote planets are designed to com- 
pensate for the small amount of light their primaries 
receive from the sun, owing to their great distance 
from that luminary. 

2. The average density of the first group consid- 
erably exceeds that of the second, the approximate 
ratio being 5:1. . 

3. The mean duration of the axial rotations, or 
mean length of the day of the interior planets, is 
much longer than that of the exterior ; the average 
in the former case being about twenty-four hours, 
but in the latter only about ten hours. 

The Properties of the Ellipse. — In the figure, S 



bo THE SOLAK SYSTEM. 

and S' are the foci of the ellipse ; AC is the major 
axis ; BD, the minor or conjugate axis ; O, the centre : 
or, astronomically, OA is the semi-axis-major or mean 
distance, OB the semi-axis-minor: the ratio of OS 
to OA is the eccentricity ; the least distance, SA, is 
the jperihdion distance ; the greatest distance, SO, 
the aphdion distance. 

Fig. 14. 




AN ELLIPSE. 



ChAEACTERISTICS of PLANETAEY CEBIT. — It will not 
be difficult to follow in the mind the additional 



Fig. 15. 




PLANETAKY ORBITS. 



characteristics of a planet's orbit. The orbit or 
elHpse just given is laid on a plane surface. Now, 



THE PLANETS. by 

iQcline it slightly, as compared with some other 
fixed plane ring, as in the cut. The astronomical 
fixed plane is the ecliptic. Imagine a planet follow- 
LDg the inclined ellipse ; at some point it must rise 
above the level of the fixed plane : this point is 
called the ascending nodcy and the opposite point of 
intersection is termed the descending node. A line 
connecting the two nodes is called the line of the 
nodes. The longitude of the node is its distance from 
the first point of Aries, measured on the ecliptic. 
Following this method, we can get a very correct 
idea of a planetary orbit in space. 

CoMPAEATiVE SiZE OP Planets. (Chambers.) — The 
following scheme will assist in obtaining a correct 
notion of the magnitude of the planetary system. 
Choose a level field or common ; on it place a globe 
two feet in diameter for the Sun : Vulcan will then 
be represented by a small pin's head, at a distance 
of about 27 feet from the centre of the ideal sun ; 
Mercury by a mustard-seed, at a distance of 82 
feet ; Yenus by a pea, at a distance of 142 feet ; the 
Earth, also, by a pea, at a distance of 215 feet ; 
Mars by a small pepper-corn, at a distance of 327 
feet ; the minor planets by grains of sand, at dis- 
tances varying from 500 to 600 feet. If space will 
permit, we may place a moderate-sized orange 
nearly one-quarter of a mile distant from the start- 
ing point to represent Jupiter ; a small orange two- 
fifths of a mile for Saturn ; a full-sized cherry three- 
quarters of a mile distant for Uranus ; and lastly, a 



70 THE SOLAR SYSTEM. 

plum 1| miles off for Neptune, the most distant planet 
yet known. Extending this scheme, we should find 
that the apheHon distance of Encke's comet would 

Fig. 16. 




COMPAKATIVE SIZE OF PLANETS. 

be at 880 feet; the aphelion distance of Donati's 
comet of 1858 at 6 miles ; and the nearest fixed star 
at 7,500 miles. 



THE PLANETS. 71 

According to this scale, the daily motion of 
Vulcan in its orbit would be 4| feet ; of Mercury, 3 
feet ; of Yenus, 2 feet ; of the Earth, 1| feet ; of 
Mars, IJ feet ; of Jupiter, lOJ inches ; of Satui-n, 
7J inches ; of Uranus, 5 inches ; and of Neptune, 4 
inches. This illustrates the fact that the orbital 
velocity of a planet decreases as its distance from 
the sun increases. 

Conjunctions of Planets. — The grouping together 
of two or more planets within a limited area of the 
heavens is a rare event. The earliest record we 
have is the one of Chinese origin, already mentioned 
on page 16, wherein it is stated that a conjunction of 
Mars, Jupiter, Saturn, and Mercury occurred in the 

Fig. 17. 



VENUS AND JUPITER IN CONJUNCTION, JANUARY 30, 1S68. 

reign of the Emperor Chuenhio. Astronomers tell 
us that this actually took place Feb. 28, 2446 B. c, 
and that they were between 10° and 18° of Pisces. 
This was before the Deluge, so that the fact must 



72 THE SOLAR SYSTEM. 

have been afterward calculated and chronicled in 
their records. In 1859, Venus and Jupiter came so 
near each other that they appeared to the naked eye 
as one object. In 1725, Venus, Mercury, Jupiter, 
and Mars appeared in the same field of the telescope. 
Are the planets inhabited? — This question is 
one which very naturally arises, when we think of 
the planets as worlds in so many respects similar 
to our own. We can give no satisfactory answer. 
Many think that the only object God can possibly 
have in making any world is to form an abode for 
man. Our own earth was evidently fitted up, al- 
though perhaps not created, for this express pur- 
pose. Everywhere about us we find proofs of 
special forethought and adaptation. Coal and oil 
in the earth for fuel and light, forests for timber, 
metals in the mountains for machinery, rivers for 
navigation, and level plains for corn. Our own 
bodies, the air, light, and heat are all fitted to each 
other with exquisite nicety. When we turn to the 
planets, we do not know but God has other races of 
intelligent beings who inhabit them, or even entirely 
different ends to attain. Of this, however, we are 
assured, that, if inhabited, the conditions on which 
life is supported vary much from those familiar 
to us. We shall notice these more especially as we 
speak of the different planets. We shall see (1) hoAv 
they differ in Hght and heat, from seven times our 
usual temperature to less than yoW j (2) in the in- 
tensity of the force of gravity, from 2^ times that of 



THE PLANETS. 73 

^V ; (3) in the constitution of 
the planet itself, from a density | heavier than that 
of the earth to one only that of cork. The tem- 
perature sweeps downward through a scale of over 

Fiff. 18. 




SIZE UP SUN AS SEEN FROM THE PLANET!-. 

2,000 in passing from Mercury to Uranus. No hu- 
man being could reside on the former, while we 

4 



74 THE SOLAE SYSTEM. 

cannot conceive of any polar inhabitant who could 
endure the intense cold of the latter. At the sum, 
one of our pounds would weigh 27 pounds ; on our 
moon the pound weight would become only about 
2 ounces ; while on Vesta, one of the planetoids, 
a man could easily spring sixty feet in the air and 
sustain no shock. Yet while Ave speak of these 
peculiarities, we do not know what modification of 
the atmosphere or physical features may exist even 
on Mercury to temper the heat, or on Uranus to 
reduce the cold. With, however, all these diversi- 
ties, we must admit the power of an all-wise 
Creator to create beings adapted to the life and 
the land, however different from our own. The 
Power that prepared a world for us, could as easily 
and perfectly prepare one for other races. May 
it not be that the same love of diversity, which will 
not make two leaves after the same pattern nor two 
pebbles of the same size, delights in worlds peopled 
by races as diverse ? While, then, we cannot affirm 
that the planets are inhabited, analogy would lead 
us to think that they are, and that the most 
distant star that shines in the arch of heaven is 
filled with living beings under the care and govern- 
ment of Him who enlivens the densest forest 
with the hum of insects, and populates even a 
drop of water with its teeming millions of animal- 
cul^e. 

Divisions of the Planets. — The planets are di- 
vided into two classes : (1) Inferio'^, or those whose 



THE PLANETS. 75 

orbits are within that of the earth — viz., Mercury, 
Venus ; (2) Supertoi^, or those whose orbits are be- 
yond that of the earth — Mars, Jupiter, Saturn, 
Uranus, Neptune. 

Motions of a Planet as seen pkom the Sun. — 
Could we stand at the sun and watch the movements 
of the planets, they would all be seen to be revolv- 
ing with different velocities in the order of the 
zodiacal signs. But to us, standing on one of the 
planets, itseK in motion, the effect is changed. To 
an observer at the sun all the motions would be real, 
while to us many are only apparent. The position 
of a planet, as seen from the centre of the sun, is 
called its heliocentric place ; as seen from the centre 
of the earth, its geocentric place. When Yenus is at 
inferior conjunction, an observer at the sun would 
see it in the opposite part of the heavens from that 
in Avhich it would appear to him if viewed from the 
earth. 

Motions of an Infeeioe Planet. — ^An inferior 
planet is never seen by us in the part of the sky 
opposite to the sun at the time of observation. It 
cannot recede from him more than 90°, or | the 
circumference, since it moves in an orbit entirely 
enclosed by the orbit of the earth. Twice in every 
revolution it is in conjunction ( 5 ) with the sun,— an 
inferior conjunction (A) when it comes between the 
earth and the sun, and a superior conjunction (B) 
when the sun lies between it and the earth. (See 
Fig. 19.) 



76 



THE SOIAFv SYSTEM. 



When the planet attains its greatest distance east 
or west (as we see it) from the sun, it is said to be 
at its greatest elongation, or in qtiadrature ( □ ). 



Fig. 19. 




QUADRATURE AND CONJUNCTION. 



When passing from B to A it is east of the sun, 
and is *' evening star ;" while passing from A to B it 
is west of the sun, and is " morning star." An in- 
ferior planet is only visible when near quadrature, 
and never when in superior conjunction, as its hght 
is then lost in the greater brilliancy of the sun. 



THE PLANETS. 



77 



When in inferior conjunction, it sometimes passes in 
front of the sun, and appears to us as a round black 
spot swiftly moving across his disk. This is called 
a transit 




RETROGRADE MOTION. 



Retrograde motion of an inferior planet. — Suppo^^e 
the earth to be at A, and the planet at B. Now, 
while the earth is passing to F, the planet will pass 
to D — the arc AF being shorter than BD, because 
the nearer a planet is to the sun the greater its 
velocity. While the planet is at B, we locate it a 
C on the echptic, in Gemini ; but at D, it appears 
to us to be at G, in Taurus. So that the planet has 
retrograded through an entire sign on the ecliptic, 
while its course all the while has been directly for- 



78 THE SOLAR SYSTEM. 

ward in the order of the signs ; and to an observer at 
the snn, such woiild have been its motion. 

Phases of an inferior planet. — An inferior planet 
presents all the phases of the moon. At superior 
conjunction, the whole illumined disk is turned to- 
ward us ; but the planet is lost in the sun's rays : 
therefore neither Mercury nor Venus ever presents a 
full circular appearance, like the full moon. A little 
before or after superior conjunction, an inferior 

Fig. 21. 

C O 3 




PHASES OF AN LNTERIOR PLANET. 



planet may be seen with a telescope ; but the whole 
of the Kght side is not turned toward us, and so the 
planet appears gibbous, like the moon between first 
quarter and fuU. In quadrature, the planet shows 
us only one-half its illumined disk ; this decreases, 
becoming more and more crescent toward inferior 
conjunction, at which time the unillumined side is 
toward us. 

Motions of a Supeeior Planet. — The superior 
planet moves in an orbit which entirely surrounds 



THE PLANETS. 79 

that of the earth. When the earth is at E (Fig. 
22), the planet at L is said to be in opposition to the 
sun. It is then at its greatest distance from him — 
180°. The planet is on the meridian at midnight 
while the sun is on the corresponding meridian on 
the opposite side of the earth ; or the planet may be 
rising when the sun is just setting. When the 
planet is at N, it is in conjunction, and being lost in 
the sun's rays is invisible to us. 

Retrograde motion of a superior planet. — Suppose 
the earth to be at E and the planet at L, and that 
we move on to G while the planet passes on to O — 
the distance EG being longer than LO (just the 
reverse of what takes place in the movements of 
the inferior planets) ; at E, we should locate the 
planet at P on the ecHptic, in the sign Cancer ; but 
at G, it would appear to us at Q, in the sign Gemini, 
having apparently retrograded on the ecliptic the 
distance PQ, while it was all the while moving on in 
the direct order of the signs. Now, suppose the 
earth moves on to I and the planet to U, we should 
then see it at the point W, further on in the ecliptic 
than Q, which indicates direct motion again, and 
at some point near Q the planet must have appeared 
without motion. After this, it will continue direct 
until the earth has completed a large portion of her 
orbit, as we shall easily see by imagining various 
positions of the earth and planet, and then drawing 
lines as we have just done, noticing whether they 
indicate direct or retrograde motion. The greater 



80 



THE SOLAR SYSTEM. 



the distance of a planet the less it will retrograde, 
as we shall perceive by drawing another orbit out- 
side the one represented in the cut, and making the 
same suppositions concerning it as those we have 
already explained. 



Fig. 22. 




EETROGBABE MOTION OF A SUPERIOR PliANET. 

Sidereal and Synodic Eeyolution. — The interval 
of time required by a planet to perform a revolution 
from one fixed star back to it again, is termed a 
sidereal revolution {sidus, a star). 

1. The interval of time between two similar con- 



THE PLANETS. 81 

junctions of an inferior planet with the earth and 
sun is termed a synodic revokition. Were the earth 
at rest, there would be no difference between a 
sidereal and a synodic revolution, and the planet 
would come into conjunction twice in each revolution. 
Since, however, the earth is in motion, it follows 
that after the planet has completed its sidereal 
revolution, it must then overtake the earth before 
thej can both come again into the same position 
with regard to the sun. The faster a planet moves, 
the sooner it can do this. Mercury, travelling at 
the greater speed and on an inner orbit, accom- 
plishes it much quicker than Yenus. The synodic 
period always exceeds the sidereal. 

2. The interval between two successive conjunc- 
tions or oppositions of a superior planet is termed a 
synodic revolution. Since the earth moves so much 
faster than any superior planet, it follows that after 
it has completed a sidereal revolution it must then 
overtake the planet before they can come again into 
the same position with regard to the sun. The 
slower the planet moves, the sooner it can do this. 
Uranus, making a sidereal revolution in eighty-four 
years, can be overtaken more quickly than Mars, 
which makes one in less than two years. It conse- 
quently requires over a second revolution to catch up 
with Mars, -^ of one to overtake Jupiter, and but 
little over yi-g- of one to come up with Uranus. In- 
deed, the earth repasses Neptune in two days after 
it has finished a sidereal revolution. 



82 



THE SOLAB SYSTEM. 



Planets as Evening and Moening Staes. — The in- 
ferior planets are evening stars from superior to 
inferior conjunction, and the superior planets from 
opposition to conjunction. During the other half 
of their revolutions they are morning stars. 

Mercury, evening star 2 months. 



Venus, 

Mars, 

Jupiter, 

Saturn, 

Uranus, 



13 

H 

6 
6 



To avoid filling the text with a multiplicity of 
figures, many interesting items are condensed in 
tables at the close of the volume. 



YULCAN. 

Supposed Discovery. — Le Yerrier, having detected 
an error in the assumed motion of Mercury, sug- 
gested, in the fall of 1859, that there may be an 
interior planet, which is the cause of this disturb- 
ance. On this being made pubHc, M. Lescarbault, 
a French physician, and an amateur astronomer, 
stated that on March 26 of that year he had seen a 
dark body pass across the sun's disk, and that this 
might have been the unknown planet. Le Yerrier 
visited him, and found his instruments rough and 
home-made, but singularly accurate. His clock was 
a simple pendulum, consisting of an ivory ball hang- 



MERCURY. 83 

ing from a nail bj a silk thread. His observations 
were on prescription paper, covered with grease 
and laudanum. His calculations were chalked on a 
board, which he planed off to make room for fresh 
ones. Le Yerrier became satisfied that a new planet 
had been really discovered by this enthusiastic ob- 
server, and congratulated him upon his deserved 
success. On March 20, 1862, Mr. Lummis, of Man- 
chester, England, noticed a rapidly-moving, dark 
spot, apparently the transit of an inner planet. 
Many other instances are given of a somewhat sim- 
ilar character. As yet, however, the existence of 
the planet is not generally conceded. The name 
Vulcan and the sign of a hammer have been given 
to it. Its distance from the sun has been estimated 
at 13,000,000 miles, and its periodic time (its year) 
at 20 days. 

MEECUEY. 

The fleetest of the gods. Sign, a , his wand. 

Description. — Mercury is nearest to the sun of 
any of the definitely known planets. When the sky 
is very clear, we may sometimes see it, just after 
the setting of the sun, as a bright sparkling star, 
near the western horizon. Its elevation increases 
evening by evening, but never exceeds 30°.* If we 
watch it closely, we shall find that it again ap- 

* This distance varies mucli, owing to the eccentricity' of Mcr 
cmy's orbit. 



84 THE SOLAR SYSTEM. 

proaclies the sun and becomes lost in his rays 
Some days afterward, just before sunrise, we can see 
the same star in the east, rising higher each morn- 
ing, until its greatest elevation equals that which it 
before attained in the west. Thus the planet appears 
to slowly but steadily oscillate like a pendulum, to 
and fro from one side to the other of the sun. The 
ancients, deceived by this, failed to discover the iden- 
tity of the two stars, and called the morning star 
Apollo, the god of day, and the evening star Mer- 
cury, the god of thieves, who walk to and fro in the 
night-time seeking plunder. The Greeks gave to 
Mercury the additional name of " The Sparkling 
One." The astrologists lookedupon it as the malig- 
nant planet. The chemists, because of its extreme 
swiftness, applied the name to quicksilver. . The most 
ancient account that we have of this planet is given 
by Ptolemy, in his Almagest ; he states its location 
on the 15th of November, 265 B. c. The Chinese 
also state that on June 9, 118 A. D., it ^vas near the 
Beehive, a cluster of stars in Cancer. Astronomers 
tell us that, according to the best calculations, it 
was at that date within less than 1° of that group. 
On account of the nearness of Mercury to the sun, 
it is difficult to be detected.* It is said that Coper- 
nicus, an old man of seventy, lamented in his last 
moments that, much as he had tried, he had never 

* An old English writer by tlie name of Goad, in 1686, humor- 
ously termed this planet, " A squinting lacquey of the sun, whc 
seldom shows his head in these parts, as if he were in debt." 



MEKCUEY. 85 

been able to see it. In our latitude and climate, 
we can generally easily detect it if we watch for it 
at the time of its greatest elongation or quadrature, 
as given in the almanac. 

Motion est Space. — It revolves about the sun at a 
mean distance of 35,000,000 miles. Its orbit is the 
most eccentric (flattened) of any among the eight 
principal planets, so that although when in peri- 
helion it approaches to within 28,000,000 miles, in 
apheHon it speeds away 15,000,000 miles farther, or 
to the distance of 43,000,000 miles. Being so near 
the sun, its motion in its orbit is correspondingly 
rapid — viz., 30 miles per second. At this rate of 
speed, we could cross the Atlantic Ocean in two 
minutes. The Mercurial year comprises only about 
88 days, or nearly three of our months. Mercury 
revolves upon its axis in about the same time as the 
earth, so that the length of the Mercurial day is 
nearly the same as that of the terrestrial one. 
Though Mercury thus completes a sidereal revolu- 
tion around the sun in 88 days, yet to pass from one 
inferior or superior conjunction to the same again (a 
synodic revolution) requires 116 days. The reason 
of this is, as already explained, that when Mercury 
comes around to the same spot in its orbit again, 
the earth has gone forward, and it requires 28 days 
for the planet to overtake us. 

Distance erom the Earth. — This varies still more 
than its sun distance. At inferior conjunction it is 
between the earth and the sun, and its mean dis- 



86 THE SOLAK SYSTEM. 

tance from us is the difference between the distance 
of the earth and the planet from the sun : at supe- 
rior conjunction it is the sum of these distances. Its 
apparent diameter in these different positions varies 
in the same proportion as the distances, or as three 
to one. The greatest and least distances vary ac- 
cording as either planet may happen to be in aphe- 
lion or perihelion. If at inferior conjunction Mer- 
cury is in aphehon and the earth in perihelion, its 
distance from us is only 90,000,000 - 43,000,000 = 
47,000,000 miles. If at superior conjunction Mer- 
cury is in aphelion and the earth in aphehon also, 
its distance from us is 93,000,000 + 43,000,000 = 
136,000,000 miles. 

Dimensions. — Mercury is about 3,000 miles in di- 
ameter. Its volume is about -gV that of the earth — 
{. e., it would require twenty globes as large as Mer- 
cury to make one the size of the earth, or 25,000,000 
to equal the sun. Yet as it is ^ denser than the 
earth, its weight is nearly -^ that of the earth, and 
a stone let drop upon its surface would fall 7J feet 
the first second. Its specific gravity is about that 
of tin. A pound weight removed to Mercury would 
weigh only about seven ounces. 

Seasons. — As Mercury's axis is much inclined 
from a perpendicular, its seasons are peculiar. 
There are no distinct frigid zones; but large re- 
gions near the poles have six weeks continuous day 
and torrid heat, alternating with a night of equal 
length and arctic cold. The sun shines perpendic- 



MEECUEY. 87 

ularly upon the torrid zone only at the equinoxes, 
while he sinks far toward the southern horizon at 
one solstice, and as far toward the northern hori- 
zon at the other. The equatorial regions, there- 
fore, modify their temperature during each rev- 
Fig. 23 




ORBIT AND SEASONS OF MERCURY. 



olution from torrid to temperate, and the tropical 
heat is experienced alternately toward the north 
and south of what we call the temperate zones. 
There is no marked distinction of zones as with 
us, but each zone changes its character twice 
during the Mercurial year, or eight times during 
the terrestrial one. An inhabitant of Mercury 



0» THE SOLAB SYSTEM. 

must be accustomed to the most sudden and yio- 
lent yicissitudes of temperature. At one time tlie 
sun not only thus pours down its vertical rays, and in 
a few weeks after sinks far down toward the horizon, 
but, on account of Mercury's elhptical orbit, when ir 
perihelion the planet approaches so near the sun that 
the heat and light are ten times as great as that we 
receive, while in aphelion it recedes so as to reduce 
the amount to four and a haK times (the average, 
however, is seven times), — a temperature sufficient to 
turn water to steam, and even to melt many of the 
metals. This entire round of transitions is swept 
through four times during one terrestrial year. The 
relative length of the days and nights is much more 
variable than with us. The sun, apparently seven 
times as large as it seems to us, must be a magnifi- 
cent spectacle, and illumine every object with insuf- 
ferable brilliancy. The evening sky is, however, 
lighted by no moon. 

Telescopic Featuees. — Under the telescope. Mer- 
cury presents all the phases of the moon, from a 
slender crescent to gibbous, when its hght is lost 
in that of the sun. These phases prove that Mer- 
cury is spherical, and shines by the light reflected 
from the sun. When in quadrature, it can some- 
times be detected with a telescope in daylight. 
Being an inferior planet, we can never see it when 
fiill, and hence the brightest, nor when nearest the 
eaiHih, as then its dark side is turned toward us. 
Owing to the dazzling light, and the vapors almost 



VENUS. 89 

always hanging around our horizon, this planet has 
not received much attention of late ; the cuts here 
given, and the remarks concerning its physical fea- 
tures, are based upon the observations of the older 
astronomers. It is thought by some to have a 
dense atmosphere loaded with clouds, which would 
materially diminish the intensity of the sun, and 
perhaps make Mercury quite habitable. Sir "W. 
Herschel, however, emphatically denies this, and 
asserts that the atmosphere is too insignificant to 
be detected. There are some dark bands about its 
equator. It has lofty mountains, which intercept 
the light of the sun, and deep valleys plunged in 
shade. One mountain has been ascertained to be 
about ten miles in height, which is 3^^ of the di- 
ameter of the planet. The height of the Dhawa- 
laghiri of the Himalayas is less than 29,000 feet, 
or Y^Vo^ part of the earth's diameter. 

VENUS. 

The Queen of Beauty. Sign p , a looking-glass. 

Desceiption. — Yenus, the next in order to Mer- 
cury, is the most brilliant of all the planets. When 
visible before sunrise, she was called by the ancients 
Phosphorus, Lucifer, or the Morning Star, and when 
she shone in the evening after sunset, Hesperus, Yes- 
per, or the Evening Star. She presents the same 
appearances as Mercury. Owing, however, to the 
greater diameter of her orbit, her apparent oscillations 



90 THE SOLAR SYSTEM. 

are nearly 48° east and west of the sun,^ or about 
18° more than those of Mercnry. She is therefore 
seen mnch earlier in the morning and much later at 
night. She is " morning star" from inferior to supe- 
rior conjunction, and " eyening star" from superior 
to inferior conjunction. She is the most brilliant 
about five weeks before and after inferior conjunc- 
tion, at which time the planet is bright enough to 
cast a shadow at night. If, in addition, at this time 
of greatest brilliancy, Yenus is at or near her high- 
est north latitude, she may be seen with the naked 
eye in full daylight. t This occurs once in eight 
years, in which interval the earth and planet return 
to the same situation in their orbits ; eight complete 
revolutions of the earth about the sun occupying 
nearly the same time as thirteen of Yenus. This 
happened last in February, 1862. A less degree 
of brilliancy is attained once in twenty-nine months, 
under somewhat the same circumstances. 

Motion in Space. — Unlike Mercury, Yenus has 
an orbit the most circular of any of the principal 

* This distance varies but little, owing to tlie slight eccentiicity 
of Yenus's orbit. 

f Arago relates that Bonaparte, upon repaiiing to the Luxem- 
boui'g, when the Du'ectoiy was about to give him a fete, was 
much surprised at seeing the multitude paying more attention to 
the heavens above the palace than to him or his brilliant staff. 
Upon inquiry, he learned that these curious persons were obseiv- 
ing with astonishment a star which they supposed to be that of 
the Conqueror of Italy. The emperor himself was not indifferent 
when his piercing eye caught the clear lusti'e of Venus smiling 
upon him at midday. 



VENUS. 91 

planets. Her mean distance from the sun is about 
66j000,000 miles, whicli varies at aphelion and peri- 
helion within the limits of a half million miles against 
15,000,000 miles in the case of the former planet. 
She makes a complete revolution around the sun in 
about 225 days, at the mean rate of 22 miles per 
second ; hence her year is equal to about seven and 
one half of our months. This is a sidereal revolu- 
tion, as it would appear to an observer at the sun, 
but a synodic revolution is 584 days. Mercury, we 
remember, catches up with the earth in 28 days after 
it reaches the point where it left the earth at the 
last inferior conjunction. But it takes Yenus nearly 
two and a half revolutions to overtake the earth and 
come into the same conjunction again. This grows 
out of the fact that Yenus has a longer orbit to 
travel through, and moves only about one-fifth faster 
than the earth, while Mercury travels nearly twice 
as fast. The planet revolves upon its axis in about 
24 hours ; so the day does not differ in length essen- 
tially from ours. 

Distance feom the Eaeth. — The distance of Ye- 
nus from the earth, like that of Mercury, when in 
inferior conjunction, is the difference between the 
distances'^ of these two planets from the sun, and 
when in superior conjunction the sum of these dis- 
tances. 

* Let the pupil calculate the distances of the earth and Venus 
from each other, when in perihelion and aphelion, as in the case 
of Mercury, ^See tables in Appendix.) 



92 THE SOLAR SYSTEM. 

The figure represents its apparent dimensions at 
the extreme, mean, and least distances from ns. 
The variation is nearly as the numbers 10, 18, and 
65. It would be natural to think that the planet is 
the brightest when the nearest, and thus the largest, 




EXTREME, MEAN, AND LEAST APPARENT SIZE OP VENUS. 



but we should remember that then the bright side 
is toward the sun, and the unillumined side toward 
us. Indeed, at the period of greatest brilliancy of 
which we have spoken, only about one-fourth of 
the light is visible. At this time, however, many 
observers have noticed the entire contour of the 
planet to be of a dull gTay hue, as seen in the cut. 

Dimensions.— Yenus is about 7,500 miles in diame- 
ter. The volume of the planet is about four-fifths 
that of the earth, while the density is about the same. 
A stone let fall upon its surface would fall 14 feet in 



VENUS. 93 

the first second : a poinid weight removed to its 
equator would weigh about five-sixths of a pound. 
From this we see that the force of gravity does not 
decrease exactly in proportion to the size of the 
planet, any more than it increases with the mass of 
the sun. The reason of this is, that the body is 
bi ought nearer the mass of the small planet, and 
so feels its attraction more fully than when far out 
upon the extreme circumference of a large body, — 
the attraction increasing as the square of the dis- 
tance from the particles decreases. 

Seasons. — As the axis of Yenus is very much in- 
clined from a perpendicular, its seasons are similar 
to those of Mercury. The torrid and temperate 

Fig. 25. 




VENUS AT ITS SOLSTICE. 



zones overlap each other ; the polar regions having 
alternately at one solstice a torrid temperature, and 
at the other a prolonged arctic cold. The inequality 



94 THE SOLAR SYSTEM. 

of the nights is very marked. The heat and light are 
double that of the earth, while the circular form of 
its orbit gives nearly an equal length to its four 
seasons. 

If the incKnation of its axis is 75*^, as some as- 
tronomers hold, its tropics must be 75° from the 
equator, and its polar circles 75° from the poles. 
The torrid zone is, therefore, 150° in v/idth. The 
torrid and frigid zones interlap through a space of 
60°, midway between the equator and poles. 

Telescopic Features. — Yenus, being an interior 
planet, presents, like Mercury, all the phases of the 
moon. This fact was discovered by Galileo, and was 
among the first achievements of his telescopic obser- 
vations. It had been argued against the Coperni- 
can system that, if true, Yenus should wax and wane 
Hke the moon. Indeed, Copernicus himself boldly 
declared that if means of seeing the planets more 
distinctly were ever invented, Yenus would be found 
to present such phases. Galileo, with his telescope, 
proved this fact, and, by overthrowing that objec- 
tion, again vindicated the Copemican theory. This 
planet is not sensibly flattened at the poles. It is 
thought to have a dense, cloudy atmosphere. This 
was established by the fact that at the transit of 
Yenus over the sun in 1761 and 1769, a faint ring 
of light was observed to surround the black 
disk of the planet. The evidence of an atmosphere, 
as well as of mountains, rests very much upon the 
peculiar appearance attending its crescent shape. 



VENUS. 



95 



(1.) The luminous part does not end abruptly ; on 
the contrary, its Kght diminishes gradually, which 
diminution may be entirely explained by the twi- 
light on the planet. The existence of an atmosphere 



Fiff 




CRESCENT AND SPOTS OP VENUS. 



which diffuses the rays of light into regions where 
the sun has already set, has hence been inferred. 
Thus, on Yenus, the evenings, like ours, are Hghted 
by twihght, and the mornings by dawn. (2.) The 
edge of the enlightened portion of the planet is un- 
even and irregular. This appearance is doubtless 
the effect of shadows cast by mountains. Spots 
have been noticed on its disk which are considered 
to be traceable to clouds. Indeed, Herschel thinks 
that we never see the real body of the planet, but 
only its atmosphere loaded with vapors, which may 
mitigate the glare of the intense sunshine. 

Satellites. — Venus is not known to have any 
Qfioon. 



96 THE SOLAR SYSTEM. 



THE EAUTH. 

SigB, ®, a circle with Equator and Meridian. 

The Eartli is tlie next planet we meet in passing 
outAvard from tlie snn. To the beginner, it seems 
strange enough to class our world among the heav- 
enly bodies. Theij are brilliant, while it is dark and 
opaque ; they appear Hght and airy, while it is solid 
and firm ; we see in it no motion, while they are 
constantly changing their position ; they seem mere 
points in the sky, while it is vast and extended. Yet 
at the very beginning we are to consider the earth 
as a planet shining brightly in the heavens, and 
appearing to other worlds as a star does to us : we 
are to learn that it is in motion, flying through its 
orbit with inconceivable velocity ; that it is not fixed, 
but hanging in space, held by an invisible power of 
gravitation which it cannot evade ; that it is small 
and insignificant beside the mighty globes that so 
gently shine upon us in the far-off sky; that our 
earth is only one atom in a universe of worlds, all 
firm and solid, and equally well fitted to be the abode 
of life. 

Dimensions. — The earth is not "round like a ball," 
but flattened at the poles. Its form is that of an 
oblate spheroid. Its polar diameter is about 7,899 
miles, and its equatorial about 7,925J. The com- 
pression is, therefore, about 26J miles. (See table 



THE EABTH. 



97 



in Appendix.) If we represent the earth by a globe 
one yard in diameter, the polar diameter would be 
one-tenth of an inch too long. It has been recently 



Fig. 37. 




THE EAKTH IN SPACE. 



shown that the equator itself is not a perfect circle, 

but is somewhat flattened, since the diameter which 

5 



98 THE SOLAE SYSTEM. 

r 

pierces the meridian 14° east of Greenwich is two 
miles longer than the one at right angles to it. The 
circumference of the earth is about 25,000 miles. 
Its density is about 5J times that of water. Its 
weight is 

6,069,000,000,000,000,000,000 tons. 

The inequalities of its surface, arising from build- 
ings, valleys, mountains, etc., have been likened to 
the roughness on the rind of an orange. This is 
not an exaggeration. On a globe sixteen inches ia 
diameter, the land, to be in proportion, should be 
represented by the thionest writiag-paper, the hills 
by small grains of sand, and elevated ranges by 
thick drawing-paper. To represent the deepest 
wells or mines, a scratch might be made that would 
be invisible except with a glass. The water in the 
ocean could be shown by a brush dipped in color 
and lightly drawn over the bed of the sea. * 

The Rotundity of the Eakth. — This is shown in 
various ways, among which are the following: (1) 
By the fact that vessels have sailed around the earth ;* 



* It is curious, in connection with this well-known fact, to re- 
call the arguments ui'ged by the Spanish philosophers against 
the reasoning of Columbus, when he assured them that he 
could arrive at Asia just as certainly by sailing west as 
east. " How," they asked, " can the earth be round ? If 
it were, then on the opposite side the rain would faU upward, 
trees would grow with their branches down, and eyerything 
would be topsy-turvy. Eveiy object on its surface would cer- 
tainly fall off; and if a ship by siiling west should get around 



THE EABTH. 99 

(2) when a ship is coming into port we see the masts 
first ; (3) the shadow of the earth on the moon is 
circular; (4) the polar star seems higher in the 
heavens as we pass north ; (5) the horizon expands 
as we ascend an eminence.* If we climb to the top 
of a hill, we can see further than when on the plain 
at its foot. Our eyesight is not improved ; it is only 
because ordinarily the curvature of the earth shuts 
off the view of distant objects, but when we ascend 
to a higher point, we can see farther over the side 
of the earth. The curvature is eight inches per 
mile, 2' x S'"^ = 32 inches for two miles, 3^ x 8^°- for 
three miles, etc. An object of these respective 
heights would be just hidden at these distances. 

Appaeent and eeal Motion. — In endeavoring to 
understand the various appearances of the heavenly 
bodies, it is well to remember how in daily life we 
transfer motion. On the cars, when in rapid move- 
ment, the fences and trees seem to glide by us, 

there, it would never be able to climb up the side of the earth 
and get back again. How can a ship sail up hill ?" 

* The histoiy of aeronautic adventure affords a curious illustra- 
tion of this same principle. The late Mr. Sadler, the celebrated 
aeronaut, ascended on one occasion in a balloon from Dublin, 
and was wafted across the Irish Channel, when, on his approach 
to the Welsh coast, the balloon descended nearly to the surface 
of the sea. By this time the sun was set, and the shades of even- 
• mg began to close in. He threw out nearly all his ballast, and 
suddenly sprang upward to a great height, and by so doing 
brought his horizon to dip below the sun, producing the whole 
phenomenon of a western sunrise. Subsequently descending in 
Wales, he, of course, witnessed a second sunset on the same 
evening. 



100 THE SOLAK SYSTEM. 

while we sit still and watch them pass. On a 
bridge, when we are at rest, we follow the undula- 
tions of the waves, until at last we come to think 
that they are stationary and we are sweeping down 
stream. "In the cabin of a large vessel going 
smoothly before the wind on still water, or drawn 
along a canal, not the smallest indication acquaints 
us with the ' way it is making.' We read, sit, 
walk, as if we were on land. If we throw a ball 
into the air, it falls back into our hand ; if we drop 
it, it ahghts at our feet. Insects buzz around us 
as in the free air, and smoke ascends in tne same 
manner as it would do in an apartment on shore. 
If, indeed, we come on deck, the case is in some 
respects different ; the air, not being carried along 
with us, drifts away smoke and other light bodies 
such as feathers cast upon it, apparently in the 
opposite direction to that of the ship's progress; 
but in reality they remain at rest, and we leave 
them behind in the air."* 

DlUENAL EeVOLUTION OF THE EaRTH AEOUND ITS 

Axis. — The earth, in constantly turning from west 

* " And what is the earth itself but the good ship we are sailing 
in through the universe, bound round the sun ; and as we sit 
here in one of the 'berths,' we are unconscious of there being 
any 'way' at all upon the vessel. On deck, too, out in the open 
air, it's all the same as long as we keep our eyes on the ship;- 
but immediately we look over the sides — and the horizon is but 
the 'gunwale' of our vessel — we see the blue tide of the great 
ocean around us go drifting by the ship, and sparkling with its 
million stars as the waters of the sea itself sparkle at night be- 
tween the tropics." 



THE EABTH. 101 

to east, elevates our horizon above the stars on 
the west, and depresses it below the stars on the 
east. As the horizon appears to us to be sta- 
tionary, we assign the motion to the stars, think- 
ing those on the west which it passes over and 
hides to have sunk below it or set, and imagining 
those on the east it has dropped below to have 
moved above it or risen. So, also, the horizon is 
depressed below the sun, and we call it sunrise; 
it is elevated above the sun, and we call it sunset 
"We thus see that the diurnal movement of the sun 
by day and stars by night is a mere optical delu- 
sion — that here as elsewhere we simply transfer 
motion. This seems easy enough for us to under- 
stand, because the explanation makes it so simple ; 
but it was the " stone of stumbling" to ancient as- 
tronomers for two thousand years. Copernicus him- 
seK, it is said, first thought of the true solution while 
riding on a vessel and noticing how he insensibly 
transferred the movement of the ship to the objects 
on the shore. How much grander the beautiful 
simpHcity of this theory than the cumbersome com- 
plexity of the old Ptolemaic beHef ! 

Diurnal motion of the Sun. — The explanation 
just given illustrates the apparent motion of the 
sun, and the cause of day and night. Suppose S to 
be the sun. E, the earth, turning upon its axis 
EF from west to east, has half its surface only illu- 
minated at one time by the sun. To a person at 
D, the sun is in the horizon and day commences. 



102 



THE SOLAB SYSTEM. 



the luiQinary appearing to rise higher and higher 
in the heavens with a westerly motion, as the ob- 
server is carried forward easterly by the earth's 
diurnal rotation to A, where he has the sun in his 



Fig. 28. 




' /'l!<H\pv^^^ 




DAILT MOTION OF THE SITN. 



meridian, and it is consequently noon. The sun 
then begins to decline in the sky until the specta- 
tor arrives at B, where it sets, or is again in the 
horizon on the west side, and night begins. He 
moves on to C, which marks his position at midnight, 
the sun being then on the meridian of places on 
the opposite part of the earth, and he is then brought 
round again to D, the point of sunrise, when another 
day commences. (Hind.) 

The unequal rate of diurnal motion. — Different 
points upon the surface of the earth revolve with 
different velocities. At the two poles the speed of 
rotation is nothing, while at the equator it is great- 
est, or over 1,000 miles per hour. At Quito, the 
circle of latitude is much longer than one at the 
mouth of the St. Lawrence, and the velocities vary 
in the same proportion. The former place moves 



THE EAETH. 103 

at the rate of about 1,038 miles per hour ; the lat- 
ter, 450 miles. In our latitude (41°) the speed is 
about 780 miles per hour. We do not perceive 
this wonderful velocity with which we are flying 
through the air, because the air moves with 
us.* Yet were the earth suddenly to stop its 
rotation, the terrible shock would, without doubt, 
destroy the entire race of man, and we, with houses, 
trees, rocks, and even the oceans, in one confused 
mass, would be hurled headlong into space. On 
the other hand, were the rate of rotation to increase, 
the length of the day would be proportionately short- 
ened, and the weight of all bodies decreased by the 
centrifugal force thus produced. Indeed, if the 
rotary movement should become swift enough to 



* An ingenious inventor once suggested that we should utilize 
the earth's rotation, as the most simple and economical, as well 
as rapid mode of locomotion that could he conceived. This was 
to he accomplished by rising in a balloon to a height inacces- 
sible to aerial currents. The balloon, remaining immovable in 
this calm region, would simply await the moment when the 
earth, rotating underneath, would present the place of destination 
to the eyes of travellers, who would then descend. A well- 
regulated watch and an exact knowledge of longitudes would 
thus render travelling possible from east to west, all voyages 
north or south naturally being interdicted. This suggestion has 
only one fault ; it supposes that the atmospheric strata do not 
revolve with the earth. Upon that hypothesis, since we rotate 
in our latitude with the velocity of 333 yards in a second, there 
would result a wind in the contraiy direction ten times more 
violent than the most terrible humcane. Is not the absence of 
such a state of things a convincing proof of the participation of 
the atmospheric envelope in the general movement ? (Guillemin.) 



104 



THE SOLAR SYSTEM. 



reduce the day to 84 minutes, or about Jy its pres- 
ent length, the force of gravity would be entirety 
overcome, and all bodies would be without weight ; 
and if the speed were still further increased, aU 
loose bodies would fly off from the earth like water 
from a grindstone when swiftly turned, while we 
should be compelled to constantly " hold on" to 
avoid sharing the same fate. But against such a 
catastrophe we are assured by the immutability of 
God's laws. " He is the same yesterday, to-day, 
and forever." The earth has not varied in its revo- 
lution Yhj oi a second in 2,000 years. 






Unequal diurnal orbits of the stars. — Let O repre- 
sent our position on the earth's surface, E Z B our 
meridian ; E I B K our horizon ; P and P' the north 



THE EAKTH. 105 

and south poleo, Z the zenith, 71 the nadir; and 
GICK the celestiaL equator. Now PB, it will be 
seen, is the elevation of the north pole above the 
horizon, or the latitude of the place. Suppose we 
should see a star at A, on the meridian below the 
pole. The earth revolves in the direction GIC ; the 
star will therefore move along A L to Z, when it is 
on the meridian above the pole. It continues its 
course along the dotted line around to A again, when 
it is on the meridian below the pole, having made a 
complete circuit around the pole, but not having 
descended below our horizon. A star rising at B 
would just touch the horizon ; one at I would move 
on the celestial equator, and would be above the 
horizon as long time as it is below — twelve hours in 
each case ; a star rising at M, would just come above 
the horizon and set again at N. 

Unequal diurnal velocities of the stars. — The stars 
appear to us to be set in a concave sheU which ro- 
tates daily about the earth. As different parts of 
the earth really revolve with varying velocities, so 
the stars appear to revolve at different rates of speed. 
Those near the pole, having a small orbit, revolve 
very slowly, while those near the celestial equator 
move at the greatest speed. 

Appearance of the stars at different places on the 
earth. — ^Were we placed at the north pole, Polaris 
would be directly overhead, and the stars would 
seem to pass around us in circles parallel to the 
horizon, and increasing in diameter from the upper 

5* 



106 THE SOLAE SYSTEM. 

to lower ones. Were Tve placed at the equator, the 
pole-star would be at the horizon, and the stars 
would move in circles exactly perpendicular to the 
horizon, and decreasing in diameter, north and south 
from those in the zenith, while we could see one 
lialf of the path of each star. Were we placed in the 
southern hemisphere, the circumpolar stars would 
rotate about the south pole, and the others in cir- 
cles resembling those in our sky, only the points of 
direction would be reversed to correspond with the 
pole. Were we placed at the south pole, the ap- 
pearance would be the same as at the north pole, 
except that there is no star to mark the direction of 
the earth's axis. 

Motion of the Eaeth ds Space about the Sun. — 
The earth revolyes in an elliptical path about the 
sun at a mean distance of 91J million of miles. This 
path is called the ecliptic : its eccentricity is about 
3,000,000 miles ; — this changes shghtly, not more 
than yTTn^roTr per centuiy, so that in time the orbit 
would become circular, were it not that after the 
lapse of some thousands of years, the eccentricity 
will begin to increase again, and will thus vary 
through all ages within definite, although yet un- 
determined limits. Its entii'e circumference is near- 
ly 600,000,000 miles, and the earth pursues this 
wonderful journey at the rate of 18 miles per second. 
This revolution of the earth about the sun gives rise 
to various phenomena, of which we shall now proceed 
to speak. 



THE EABTH. 



107 



1. Change in the appearance of the heavens in differ- 
ent months. — This is the natural result of the revolu- 
tion of the earth about the sun. In Fig. 30, suppose 



Fig. 30. 



* ¥ 



* 



* 
** 










**« 



* 



P 

APPEABANCB OF THE HEAVENS IN DITPERENT SEASONCi 



A B C D to be the orbit of the earth, and E F G 
H the sphere of the fixed stars, surrounding the 
sun in every direction. When our globe is at A, the 
stars about E are on the meridian at midnight. 
Being seen from the earth in the opposite quarter 



108 THE SOLAR SYSTEM. 

to the sun, they are most favorably placed for obser- 
vation. The stars at G, on the contrary, will be invisible, 
for the sun intervenes between them and the earth : 
they are on the meridian of the spectator about the 
same time as the sun, and are always hidden in his 
rays. In three months the earth has passed over 
one-fourth of her orbit, and has arrived at B. Stars 
about F now appear on the meridian at midnight, 
while those at E, which previously occupied their 
places, have descended toward the west and are 
becoming lost in the sun's refulgence, while those 
about G are just coming into sight in the east. In 
three months more the earth is situated at C, and 
stars about G shine in the midnight sky, those at F 
having, in their turn, vanished in the west. Stars 
at E are on the meridian at noon, and consequently 
hidden in daylight; and those about H are just 
escaping from the sun's rays, and commencing their 
appearance in the east. One revolution of the 
earth brings the same stars again on the meridian 
at midnight. Thus it is that the earth's motion 
round the sun as a centre explains the varied aspect 
of the heavens in the summer and winter skies. 
(Hind.) 

2. Yearly path of the sun through the heavens. — ^We 
have spoken of the diurnal motion of the sun. We 
now speak of its second apparent motion — ^its yearly 
path among the stars."^ If we look at the accom- 

* This yearly movement of tlie smi among the fixed stars is 
not as appai'ent to us as his daily motion, because his superior 



THE EARTH. 109 

panying plate (Fig. 31), we can see how the motion 
of the earth in its orbit is also transferred to the 
sun, and causes him to appear to us to travel in a 
fixed path through the heavens. When the earth ia 
in any part of the ecliptic, the sun seems to us to be 
in the point directly opposite. For example, when 
the earth is in Libra (=^)* — autumnal equiaox — tiiC 
sun is in Aries («f) — vernal equinox; when the sun 
enters the next sign, Taurus ( « ), the earth in fact 
has passed on to Scorpio (^). Thus as the earth 
moves through her orbit, the sun seems to pass 
through the same path along the opposite side of the 
ecliptic, making the entire circuit of the heavens in 
the year, and returning at the end of that time to the 
same place among the stars. If the earth could leave 
a shining line as it passes through its orbit about the 
sun, we should see the sun apparently moving along 
this same line on the opposite side of the circle. 
We therefore define the ecliptic as the real orbit of 
the earth about the sun, or the apparent path of the sun 
through tJw heavens. The ecliptic crosses the celes- 
tial equator at two points. These are called the 
equinoxes. 

light blots out the stars. But if we notice a star at the western 
horizon just at sunset, we can tell what constellation the sun is 
then in: now wait two or three nights, and we shall find that star 
is set, and another has taken its place. Thus we can trace the 
sun through the year in his path among the fixed stars. 

* When we say " the earth is in Libra," we mean that a spec- 
tator placed at the sun would see the earth in that part of the 
heavens which is occupied by the sign Libra. 



110 THE SOLAB SYSTEM. 

3. An apparent movement of the sun, north and 
south. — Having now spoken of the apparent diurnal 
and annual motions of the sun, there yet remains a 
third motion, which has doubtless oftentimes at- 
tracted our attention. In summer, at midday, the 
sun is high in the heavens ; in the winter, quite low, 
near the southern horizon. In summer he is a long 
time above the horizon ; in the winter, a short time. 
In summer he rises and sets north of the east and 
west points ; in winter, south of the east and west 
points. This subject is so intimately connected with 
the next, that we shall understand it best when taken 
in connection with it. 

4. Change of the Seasons. — Yabiation in Length 
OF Day and Night. — By closely studying the accom- 
panying illustration and imagining the various posi- 
tions of the earth in its orbit, let us try to under- 
stand the several points. 

I. Obliquity of the ecliptic. — The axis of the earth 
is inclined 23J° from a perpendicular to its orbit. 
This angle is called the obHquity of the ecliptic. 

H. Parallelism of the axis. — In all parts of the 
orbit, the axis of the earth is parallel to itseK and 
constantly points toward the North Star.* This is 
only an instance of what is very familiar to us all. 
Nature reveals to us nothing more permanent than 
the axis of rotation in anything that is rapidly 
turned. It is its rotation which keeps a boy's hoop 

* There is a slight variation ft'om this, which we shall soon 
notice. 



Ill 




112 THE SOLAR SYSTEM. 

from falling. For the same reason a quoit retains 
its direction when whirled, and it will keep in the 
same plane at whatever angle it may be thrown. 
A man slating a roof wishes to throw a slate to the 
ground ; he simply whirls it, and as it descends it 
will strike on the edge without breaking. As long 
as a top spins there is no danger of its falling, 
since its tendency to preserve parallel its axis of 
rotation is greater than the attraction of the earth. 
This wonderful law would lead us to think that 
the axis of the earth always points in the same 
direction, even if we did not know it from direct 
observation. 

III. The rays of the sun strike the various 'por- 
tions of the earth, when in any position, at different 
angles. — Example. "When the earth is in Libra, and 
also when in Aries, the rays strike vertically at the 
equator, and more and more obHquely in the northern 
and southern hemispheres, as the distance from the 
equator increases, until at the poles they strike 
almost horizontally. This variation in the direction 
of the rays produces a corresponding variation in 
the intensity of the sun's heat and Hght at dif- 
ferent places, and accounts for the difference between 
the torrid and polar regions. 

IV. As the earth changes its position the angle at 
which the rays strike any portion is varied. — Ex- 
ample. Take the earth as it enters Capricornus 
(s5) and the sun in Cancer (©) He is now over- 
head, 23|° north of the equator. His rays strike 



THE EARTH. 113 

less obliquely in the northern hemisphere than 
when the earth was in Libra. Let six months 
elapse : the earth is now in Cancer and the sun in 
Capricomus; and he is overhead, 23 J° south of 
the equator. His rays strike less obliquely in the 
southern hemisphere than before, but in the northern 
hemisphere more obliquely. These six months have 
changed the direction of the sun's rays on every 
part of the earth's surface. This accounts for the dif- 
ference in temperature between summer and winter. 

V. The Equinoxes. — At the equinoxes one half 
of each hemisphere is illuminated: hence the 
name Equinox {cequus, equal, and nox, night). At 
these points of the orbit the days and nights are 
equal over the entire earth,^ each being twelve 
hours in length. 

VI. Northern and southern hemispheres unequally 
illuminated, — While one half of the earth is con- 
stantly illuminated, at all points in the orbit except 
the equinoxes the proportion of the northern or 
southern hemisphere which is in daylight or dark- 
ness varies. When more than half of a hemi- 
sphere is in the light, its days are longer than 
the nights, and vice versa, 

VII. The seasons and the comparative length of 
days and nights in the South Temperate Zone, at any 
specified time, are the reverse of those in the North 
Temperate Zone, except at the Equinoxes, where tJiey 

are alike. 

* 
* Except a small space at each pole. • 



114 THE SOLAE SYSTEM. 

Vm. The earth at the Summer Solstice. — ^When 
the earth is at the summer solstice, about the 
21st of June, the sun is overhead 23J° north of the 
equator, and if its vertical rays could leave a gold- 
en line on the surface of the earth as it revolves, they 
would mark the Tropic of Cancer. The sun is at 
its furthest northern declination, ascends the high- 
est it is ever seen above our horizon, and rises and 
sets 23 J° north of the east and west points. It seems 
now to stand still in its northern and southern course, 
and hence the name Solstice {sol, the sun, sto, to 
stand). The days in the north temperate zone 
are longer than the nights. It is our summer, and 
the 21st of June is the longest day of the year. In 
the south temperate zone it is winter, and the 
shortest day of the year. The circle that sepa- 
rates day from night extends 23^° beyond the 
north pole, and if the sun's rays could in like manner 
leave a golden line on that day, they would trace 
on the earth the Arctic Circle. It is the noon of 
the long six months polar day. The reverse is 
true at the Antarctic Circle, and it is there the 
midnight of the long six months polar night. 

IX. The earth at the Autumnal Equinox. — The 
earth crosses the aphelion point the 8th of July, 
when it is at its furthest distance from the sun, 
which is then said to be in apogee. The sun each 
day rising and setting a trifle further toward the 
south, passes through a lower circuit in the heavens 
We reach the autumnal equinox the 22d of Sep- 



THE EAETH. 115 

tember. The sun being now on the equinoctial, if 
its vertical rays could leave a line of golden light, 
they would mark on the earth the circle of the 
equator. It is autumn in the north temperate zone 
and spring in the south temperate zone. The days 
and nights are equal over the whole earth, the sun 
rising at 6 A. M. and settiug at 6 p. M., exactly in the 
east and west where the equinoctial intersects the 
horizon. 

X. The eartJi at the Winter Solstice. — The sun 
after passing the equinoctial — "crossing the line," 
as it is called — sinks lower toward the southern ho- 
rizon each day. We reach the winter solstice the 
21st of December. The sun is now directly overhead 
23J° south of the equator, and if its rays could 
leave a line of golden light they would mark on 
the earth's surface the Tropic of Capricorn. It 
is at its furthest southern declination, and rises and 
sets 23J° south of the east and west points. It 
is our winter, and the 21st of December is the short- 
est day of the year. In the south temperate 
zone it is summer, and the longest day of the 
year. The circle that separates day from night 
extends 23J° beyond the south pole, and if the sun's 
rays in like manner could leave a line of golden light 
they would mark the Antarctic Circle. It is there 
the noon of the long six months polar day. At 
the Arctic Circle the reverse is true ; the rays faU 
23 J° short of the north pole, and it is there the 
midnight of the long six months polar night. Here 



116 THE SOLAE SYSTEM. 

again the sun appears to us to stand still a day 
or two before retracing its course, and it is there- 
fore called the Winter Solstice. 

XI. The earth at the Vernal Equinox. — The earth 
reaches its 'perihelion about the 31st of December. 
It is then nearest the sun, which is therefore said 
to be in perigee. The sun rises and sets each day 
further and further north, and chmbs up higher 
in the heavens at midday. Our days gradually 
increase in length, and our nights shorten in the 
same proportion. On the 21st of March^ the sun 
reaches the equinoctial, at the vernal equinox. He 
is overhead at the equator, and the days and nights 
are again equal. It is our spring, but in the south 
temperate zone it is autumn. 

XII. The yearly path finished. — The earth moves 
on in its orbit through the spring ,and Rummer 
months. The sun continues its northerly course, 
ascending each day higher in the heavens^ and its 
rays becoming less and less oblique. On the 21st 
of June it again reaches its furthest northern decli- 
nation, and the earth i^ at the summer solstice. We 
have thus traced the yearly path, and noticed the 
course of the changing seasons, with the length of 
the days and nights. The same series has been 
repeated through all the ages of the past, and will 
be till time shall be no more. 

XIII. Distance of the earth from fJie sun varies. — 

* The precise time of the equinoxes and solstices varies each 
year, but within a small limit 



THE EARTH. 117 

W« notice, from what we have just seen, that we are 
nearer the sun by 3,000,000 miles in winter than in 
summer. The obHqueness with which the rays 
strike the north temperate zone at that time pre- 
vents our receiving any special benefit from this 
favorable position of the earth. 

Xiy. Southern summer. — The inhabitants of the 
south temperate zone have their summer whUe the 
earth is in perihelion, and the sun's rays are about 
^ warmer than when in aphelion, our summer-time. 
This will perhaps partly account for the extreme heat 
of their season. Herschel tells us that he has found 
the temperature of the surface soil of South Africa 
159° F, Captain Sturt, in speaking of the extreme 
heat of Australia, says that matches accidentally 
dropped on the ground were immediately ignited. 
The southern winters, for a similar reason, are 
colder ; and this makes the average yearly tempera- 
ture about the same as ours. 

XV. Extremes of heat and cold not at the solstices. — 
We notice that we do not have our greatest heat at 
the time of the summer solstice, nor our greatest 
cold at the winter solstice. After the 21st of June, 
the earth, already warmed by the genial spring 
days, continues to receive more heat from the sun 
by day than it radiates by night : thus its tempera- 
ture still increases. On the other hand, after the 
21st of December the earth continues to become 
colder, because it loses more heat during the night 
than it receives during the day. 



118 THE SOLAR SYSTEM. 

XVI. Summer longer than winter, — As the sun is 
not in the centre of the earth's orbit, but at one 
of its foci, that portion of the orbit which the earth 
passes through in going from the vernal to the 
Autumnal equinox comprises more than one-haK the 
entire echptic. On this account the summer is 
longer than the winter. The difference is still fur- 
ther enhanced by the variation in the earth's ve- 
locity at aphelion and perihelion. The annexed 
table gives the mean duration of the seasons : 



Days. Seasons. Days. 

Spring 92.9 Autumn 89.7 

Summer 93.6 Winter 89.0 

The difference of time in the earth's stay in the 
two portions of the ecliptic, as will be seen from the 
above, is 7.8 days. 

XVII. Varying velocity of the -earth. — We can see, 
by looking at the plate, that the velocity of the 
earth must vary in different portions of its orbit. 
When passing from the vernal equinox to aphelion, 
the attraction of the sun tends to check, its speed ; 
from that point to the autumnal equinox, the at- 
traction is partly in the direction of its motion, 
and so increases its velocity. The same principle 
applies when going to and from perihelion. 

XVTTT. Curious appearance of the sun at the north 
pole. — " To a person standing at the north pole, the 
sun appears to sweep horizontally around the sky 
every twenty-four hours, without any perceptible 



THE EAETH. 119 

variation in its distance from the horizon. It is, 
however, slowly rising, until, on the 21st of June, it 
is twenty-three degrees and twenty-eight minutes 
above the horizon, a little more than one-fourth of 
the distance to the zenith. This is the highest point 
it ever reaches. From this altitude it slowly de- 
scends, its track being represented by a spiral or 
screw with a very fine thread ; and in the course of 
three months it worms its way down to the horizon, 
which it reaches on the 22d of September. On this 
day it slowly sweeps around the sky, with its face 
half hidden below the icy sea. It still continues to 
descend, and after it has entirely disappeared it is 
stiU so near the horizon that it carries a bright 
twiUght around the heavens in its daily circuit. As 
the sun sinks lower and lower, this twilight grows 
gradually fainter, till it fades away. December 21st, 
the sun is 23° 28' below the horizon, and this is the 
midnight of the dark polar winter. From this date 
the sun begins to ascend, and after a time it is her- 
alded by a faint dawn, which circles slowly around 
the horizon, completing its circuit every twenty-four 
hours. This dawn grows gradually brighter, and 
on the 22d of March the peaks of ice are gilded 
with the first level rays of the six months day. The 
bringer of this long day continues to wind his spiral 
way upward, till he reaches his highest place on the 
21st of June, and his annual course is completed." 

XIX. HesultSf if the axis of the earth luere perpeii- 
dicular to the ecliptic. — The sun would then always 



120 THE SOLAB SYSTEM. 

appear to move through the equinoctial. He would 
rise and set every day at the same points on the 
horizon, and pass through the same circle in the 
heavens, while the days and nights would be equal 
the year round. There would be near the equator a 
fierce torrid heat, while north and south the climate 
would melt away into temperate spring, and, lastly, 
into the rigors of a perpetual winter. 

XX. Results f if the equator of the earth were jperpen- 
dicular to the ecliptic- — Were this the case, to a spec- 
tator at the equator, as the earth leaves the vernal 
equinox, the sun would each day pass through a 
smaller circle, until at the summer solstice he would 
reach the north pole, when he would halt for a time 
and then slowly return in an inverse manner. 

In our own latitude, the sun would make his 
diurnal revolutions in the way we have just de- 
scribed, his rays shining past the north pole fur- 
ther and further, until we were included in the 
region of perpetual day, when he would seem to 
wind in a spiral course up to the north star, and 
then return in a descending curve to the equator. 

Precession of the Equinoxes. — We have spoken 
of the equinoxes as if they were stationary in the 
orbit of the earth. Over two thousand years ago, 
Hipparchus found that they were falling back along 
the ecliptic. Modern astronomers fix the rate at 
about 50" of space annually. If we mark either point 
in the ecliptic at which the days and nights are equal 
over the earth, which is where the plane of the earth's 



THE EARTH. 121 

equator passes exactly through the centre of the 
sun, we shall find the earth the next year comes 
back to that position 50" (20 m. 20 s. of time) earlier. 
This remarkable effect is called the Precession of the 
Equinoxes, because the position of the equinoxes in 
any year precedes that which they occupied the year 
before. Since the circle of the ecliptic is divided 
into 360°, it follows that the time occupied by the 
equinoctial points in making a complete revolution 
at the rate of 50.2" per year is 25,816 years. 

Results of the Precession of the Equinoxes. — In Fig. 
31, we see that the line of the equinoxes is not 
at right angles to the echptic. In order that the 
plane of the terrestrial equator should pass through 
the sun's centre 50" earlier, it is necessary that the 
plane itself should slightly change its place. The 
axis of the earth is always perpendicular to this 
plane, hence it follows that the axis is not rigorously 
parallel to itself. It varies in direction, so that the 
north pole describes a minute circle in the starry 
vault twice 23° 28' in diameter. To illustrate this, 
in the cut we suppose that after a series of years the 
position of the earth's equator has changed from efh 
io g'Kl. The inchnation of the axis of the earth, C P, 
to CQ, the pole of the ecliptic, remains unchanged ; but 
as it must turn with the equator, its position is moved 
from C P to C P', and it passes slowly around through 
a portion of a circle whose centre is C Q. The dii-ec- 
tion of this motion is the same as that of the hands 
of a watch, or just the reverse of that of the revolution 



122 



THE SOLAK SYSTEM. 



of the earth itself. The position of the north pole in 
the heavens is therefore gradually but almost insen- 
sibly changing. It is now distant from the north 
polar star about 1J°. It wiU continue to approach 




CHANGE OF EAKTH's EQUATOR AND AXIS. 



it until they are not more than half a degree apart. 
In 12,000 years Lyra will be our polar star : 4,500 
years ago the polar star was the bright star in the 
constellation Draco. As the right ascension of the 
stars is reckoned eastward from the vernal equinox 
along the equinoctial, the precession of the equinoxes 
increases the E. A. of the stars 50" per year. On 
this account, star maps must be accompanied by the 
date of their calculations, that they may be corrected 
to correspond with this annual variation. The con- 
stellations are fixed in the heavens, while the signs of 



THE EAKTH. 



123 



the zodiac are not ; thej are simply abstract divisions 
of the ecliptic which move with the equinox. When 
named, the sun was in both the sign and constellation 
Aries, at the time of the vernal equinox ; but since 
then the equinoxes have retrograded nearly a whole 
sign, so that now while the sun is in the sign Aries 
on the ecliptic, it corresponds to the constellation 
Pisces in the heavens. Pisces is therefore the first 
constellation in the zodiac. (See Fig. 72.) 

Causes of the Precession of the Equinoxes. — Before 
commencing the explanation of this phenomenon, it 
is necessary to impress upon the mind a few facts. 
1. The earth is not a perfect sphere, but is swollen 
at the equator. It is like a perfect sphere covered 
with padding, which increases constantly in thick- 
ness from the poles to the equator ; this gives it a 
turnip-like shape. 2. The attraction of the sun is 

Fie:. 33. 




INFLUENCE OF THE SUN ON A MOUNTAIN NEAK THE EQUATOR. 




greater the nearer a body is to it. 3. The attraction 
is not for the earth as a mass, but for each particle 
separately. In the figure, the position of the earth 



124 THE SOLAR SYSTEM. 

at the time of tlie winter solstice is represented. 
P is the north pole, a h the ecliptic, C the centre 
of the earth, C Q a line perpendicular to the echp- 
tic, so that the angle QCP equals the obliquity 
of the ecliptic. In this position the equatorial pad- 
ding we have spoken of — the ring of matter about 
the equator — is turned, not exactly toward the 
sun, but is elevated above it. Now the attraction 
of the sun pulls the part D more strongly than 
the centre ; the tendency of this is to bring D 
down to a. In the same way the attraction for C is 
greater than for I, so it tends to draw C away from 
I, and as at the same time D tends toward a, to pull 
I up toward h. The tendency of this, one would 
think, would be to change the inclination of the axis 
C P toward C Q, and make it more nearly perpendic- 
ular to the ecKptic. This would be the result if the 
earth were not revolving upon its axis. Let us con- 
sider the case of a mountain near the equator. This, 
if the sun did not act upon it, would pass through 
the curve H D E in the course of a semi-revolution of 
the earth. It is nearer the sun than the centre C is ; 
the attraction therefore tends to pull the mountain 
downward and tilt the earth over, as we have just 
described; so the mountain will pass through the 
curve H/^, and instead of crossing the ecKptic at E 
it will cross at ^ a little sooner than it otherwise 
would. The same influence, though in a less degree, 
obtains on the opposite side of the earth. The 
mountain passes around the earth in a curve nearer 



THE EARTH. 



1^5 



to h, and crosses the ecliptic a little earlier. The 
same reasoning will apply to each mountain and to 
all the protuberant mass near the equatorial regions. 
The final effect is to turn sHghtly the earth's equator 
so that it intersects the ecliptic sooner than it would 
were it not for this attraction. At the summer sol- 
stice the same tilting motion is produced. At the 
equinoxes the earth's equator passes directly through 
the centre of the sun, and therefore there is no ten- 
dency to change of position. As the axis C P must 
move with the equator, it slowly revolves, keeping 
its inclination unchanged, around C Q, the pole of 
the ecliptic, describing, in about 26,000 years, a 
minute circle twice 23° 28' in diameter. 

Precession illustrated in the spinning of a top. — This 
motion of the earth's axis is most singularly illus- 
trated in the spinning 
of a top, and the more 
remarkably because 
there the forces are of 
an opposite character to 
those which act on the 
earth, and so produce 
an opposite effect. "We 
have seen that if the 
earth had no rotation, the 
sun's attraction on the 
" padding" at the equator Avould bring C P nearer 
to C Q, but that in consequence of this rotation the 
effect really produced is that CP, the earth's axis, 




SPINNING OF A 



126 THE SOLAK SYSTEM. 

slowly revolves around C Q, the pole of the heavens, m 
a direction opposite to that of rotation. 

In Fig. 34, let C P be the axis of a spianing top, 
and C Q the vertical Une. The direct tendency of 
the earth's attraction is to bring C P furtlier. from 
C Q (or to make the top fall), and if the top weriB 
not spinning this would be the result ; but in 
consequence of the rotary motion the incHnation 
does not sensibly alter (until the spinning is retarded 
by friction), and so C P slowly revolves around C Q 
in the same direction as that of rotation. 

Nutation (nutatio, a nodding). — We have noticed 
the sun as producing precession ; the moon has, 
however, treble its influence ; for although the 
moon's mass is not -2-0,^-0,-^017 P^^* that of the sun, 
yet she is 400 times nearer and her attraction is cor- 
respondiagly gi'eater. The moon's orbit does not lie 
parallel to the ecliptic, but is incHned to it. Now 
the sun attracts the moon, and disturbs it as he 
would the path of the mountain we have just sup- 
posed, and the effect is the same — viz., the intersec- 
tions of the moon's orbit with the ecHptic travel 
backward, completing a revolution in about 18 
years. During half of this time the moon's orbit is 
inclined to the ecliptic in the same way as the 
earth's equator ; during the other half it is inclined 
in the opposite way. In the former state, the 
moon's attractive tendency to tilt the earth is very 
s air 11, and the precession is slow ; in the latter, the 
tendency is great, and precession goes on rapidly. 




PATH OF THE NORTH POLE 



THE EAETH. 127 

The consequence of this is, that the pole of the 
earth is irregularly shifted, so Fig. 35. 

that it trayels in a slightly 
curved line, giving it a kind of 
"wabbling" or " nodding" mo- 
tion, as shown — though greatly 
exaggerated — in Fig. 35. The 
obliqnity of the ecliptic, which 
we consider 23° 28', is the mean 
of the irregularly curved line i^ the heavens. 
and is represented by the dotted circle. 

Periodical change in the obliquity of the ecliptic. — 
Although it is sufficiently near for all general pur- 
poses to consider the obliquity of the ecliptic invari- 
able, yet this is not strictly the case. It is subject 
to a small but appreciable variation of about 46" 
per century. This is caused by a slow change of 
the position of the earth's orbit, due to the attraction 
of the planets. The effect of this movement is to 
gradually diminish the inclination of the earth's 
equator to the ecliptic (the obliquity of the ecliptic). 
This will continue for a time, when the angle will as 
gradually increase ; the extreme limit of change 
being only 1° 21'. The orbit of the earth thus 
vibrates backward and forward, each oscillation 
requiring a period of 10,000 years. This change 
is so intimately blended, in its effect upon the 
obliquity of the ecliptic, with that caused by pre- 
cession and nutation, that they are only separable 
in theory ; in point of fact, they all combine to 



128 THE SOLAE SI STEM. 

produce the waying motion we have already de- 
scribed. As a consequence of this variation in the 
obliquity of the ecliptic, the sun does not come as 
far north nor decline as far south as at the Creation, 
while the position of all the terrestrial circles — 
Tropic of Cancer, Capricorn, Arctic, etc. — is con- 
stantly but slowl}' changing. Besides this, it tends 
to vary slightly the comparative length of the 
days and nights, and, as the obHquity is now dimin- 
ishing, to equalize them. As the result of this vari- 
ation in the position of the orbit, some stars which 
were formerly just south of the ecUptic are now 
north of it, and others that were just north are now 
a little further north ; thus the latitude of these 
stars is gradually changing. 

Change in the major axis (line of apsides) of the 
earth's orhit. — Besides all the changes in the posi- 
tion of the earth in its orbit due to precession, the 
line connecting the aphelion and perihelion points 
of the orbit itseK is slowly moving. The conse- 
quence of this is a variation in the length of the 
seasons at different periods of time. In the year 
4089 B. c, about the supposed epoch of the crea- 
tion, the sun was in perigee at the vernal equi- 
nox, so that the summer and autumn seasons were 
of equal length, but longer than the Tvdnter and 
spring seasons, which were also equal.^ In the 



* The sun is said to be in perig.^e at any point in the orbit, 
when the earth is at perihelion at the same point ; in other 



THE EAETH. 129 

year 1250 A. d., the sun was in perigee when the 
earth was at the winter solstice, about Christmas, 
instead of ten days after as now ; the spring quarter 
was therefore equal to the summer one, and the 
autumn quarter to the winter one, the former being 
the longer. In the year 6589 A. D., the sun will be 
in perigee when the earth is at the autumnal equi- 
nox; summer will then be equal to autumn and 
winter to spring, the former seasons being the 
shorter. In the year 11928 A. D., the sun will be 
in perigee when the earth is at the summer solstice : 
finally, in 17267 A. d., the cycle will be completed, 
and for the first time since the creation of man the 
vernal equinox will coincide with the solar perigee 
Permanence in the midst of change. — We thus 
see that the ecliptic is constantly modifying its ellip- 
tical shape ; that the orbit of the earth slowly oscil- 
lates upward and downward ; that the north pole 
steadily turns its long index-finger over a dial that 
marks 26,000 years ; that the earth, accurately 
poised in space, yet gently nods and bows to the 
attraction of sun and moon. Thus changes are con- 
tinually taking place that would ultimately entirely 
reverse the order of nature. But each of these has 
its bounds, beyond which it cannot pass. The 
promise made to man after the Deluge, is that 
" while the earth remaineth, seed-time and harvest, 
and cold and heat, and summer and winter, and 

words, the sim's perigee corresponds with the earth's perihelion, 
and the sun's apogee to the earth's aphelion. 



130 



THE SOLAE SYSTEM. 



day and night shall not cease." The modem dis- 
coveries of astronomy prove conclusively that the 
seasons are to be permanent ; that the Creator, 
amid all these transitions, has ordained the means 
of carrying out His promise through all time. 

Refkaction. — The atmosphere extends above the 
earth about 500 miles. Near the surface it is 
dense, while in the upper regions it is exceedingly 
rare. The rays of light from the heavenly bodies 




REFRACTION. 



passing through these different layers are turned 
downward toward a perpendicular more and more 
as the density increases. According to a well- 
known law of optics, if the ray of light from a star 
were bent in fifty directions before entering the eye, 
the star would nevertheless appear to be in the line 
of the one nearest the eye. The effect of this is, 
that the apparent place of a heavenly body is higher 



THE EAETH. 



131 



than the true place. This is illustrated in Fig. 36. 
The sun at S, were it not for the atmosphere, would 
send a direct ray to L. Instead, the ray at A is 
refracted downward, and would then enter the eye 
at N ; passing, however, through a layer of a differ- 
ent density, at B it is again bent, and meets the eye 
of the observer at C. He sees the sun, not in the 
direction of the curved line CBAS, but that of the 
straight line CBS. 

The amount of refraction varies with the tempera- 
ture, moisture, and other conditions of the atmos- 
phere. It is zero for a body in the zenith, and 
increases gradually toward the horizon (as the thick- 
ness of the intervening atmosphere increases), where 
it is about 33'. 



Fig. 37. 




Change of place and appearance of tlie-sun and moon, 
-The sun may be reallv below the horizon, and yet 



132 THE SOLAR SYSTEM. 

seem to be above it. For example, on April 20, 
1837, the moon was eclipsed before the sun had 
set. The mean diameter of both the sun and moon 
being rather less than 33', it foUows that when 
we see the lower edge of either of these lumina- 
ries apparently just touching the horizon, in reality 
the whole disk is completely helow it, and would 
be altogether hidden were it not for the effect 
of refraction. The day is consequently materially 
lengthened. 

The sun and moon often appear flattened when 
near the horizon. This is easily accounted for on 
the principle just stated. The rays from the lower 
edge pass through a denser layer of the atmosphere, 
and are therefore refracted about 4' more than those 
from the upper edge : the effect of this is to make 
the vertical diameter appear about 4' less than the 
horizontal, and so distort the figure of the disk into 
an OYal shape. 

The sun and moon often appear larger when near 
the horizon than when high in the sky. This is not 
caused by refraction, but is a mere error of judg- 
ment. At the horizon we compare them with va- 
rious terrestrial objects which lie between them and 
us, while aloft we have no association to guide us, 
and we are led to underrate their size. On looking 
at them through a tube, the illusion disappears. 
The moon should naturally appear largest when 
at a great altitude, as it is then at a less distance 
from us. 



THE EARTH. 133 

The dim and hazy appearance of the heavenly 
bodies when near the horizon is caused not only by 
the rays of light having to pass through a larger 
space in the atmosphere, but also by their travers- 
ing the lower and denser part. It is estimated that 
the solar light is diminished 1,300 times in passing 
through the lower strata. Therefore we are enabled 
to gaze upon the sun at that time without being 
dazzled by his brilliant beams. 

TiviligTd. — The glow of light after sunset and 
before sunrise, which we term Uviliglit, is caused by 
the refraction and reflection of the sun's rays by the 
atmosphere. For a time after the sun has truly set, 
the refracted rays continue to reach the earth ; but 
when these have ceased, he still continues to illumi- 
nate the clouds and upper strata of the air, just as 
he may be seen shining on the summits of lofty 
mountains long after he has disappeared from the 
view of the inhabitants of the plains below. The 
air and clouds thus illuminated reflect back part 
of the light to the earth. As the sun sinks lower, 
less light reaches us until reflection ceases and 
night ensues. The same thing occurs before sun- 
rise, only in reverse order. The duration of twilight 
is usually reckoned to last until the sun's depres- 
sion below the horizon amounts to 18° ; this, how- 
ever, varies with the latitude, seasons, and condi- 
tion of the atmosphere. Strictly speaking, in the 
latitude of Greenwich there is no true night for a 
month before and after the summer solstice, but 



134 THE soLAE syste:m:. 

constant twilight from sunset to sunrise. The sun 
is then near the Tropic of Cancer, and does not 
descend so much as 18° below the horizon during 
the entire night. The twilight is shortest at the 
equator and longest toward the poles, where the 
night of six months is shortened by an evening 
twilight of about fifty days and a morning one of 
equal length. 

Diffused light. — The diffiised light of day is pro- 
duced in the same manner as that of twilight. The 
atmosphere reflects and scatters the sunlight in 
every direction. Were it not for this, no object 
would be visible to us out of direct sunshine ; every 
shadow of a passing cloud would be pitchy dark- 
ness ; the stars would be visible all day ; no window 
would admit light except as the sun shone directly 
through it, and a man would require a lantern to go 
around his house at noon. This is illustrated very 
clearly in the rarified atmosphere of elevated re- 
gions, as on Mont Blanc, where it is said the glare 
of the direct sunlight is almost insupportable ; the 
darkness of the shadows is deeper and denser ; all 
nice shading and coloring disappear; the sky has 
a blackish hue, and the stars are seen at midday. 
The blue Hght reflected to our eyes from the atmos- 
phere above us, or more probably from the vapor in 
the air, produces the optical delusion we call the 
sky. Were it not for this, every time we cast our 
eyes upward we should feel like one gazing over a 
dizzy. precipice ; while now the crystal dome of blue 



THE EARTH. 135 

smiles down upon us so lovingly and beautifully 
that we call it heaven. 

Abeeeation of Light. — We have seen that the 
places of the heavenly bodies are apparently changed 
by refraction. Besides this, there is another change 
due to the motion of light, combined with the mo- 
tion of the earth in its orbit. For example : the 
mean distance of the earth from the sun is ninety- 
one and a half miUions of miles, and since light 
travels 183,000 miles per second, it follows that the 
time occupied by a ray of light in reaching us from 
the sun is about 8J min. ; so that, in point of fact, 
when we look at the sun (1), we do not see it as 
it is, but as it was 8 J min. since. If our globe 
were at rest, this would be well enough, but pince 
the earth is in motion, when the ray enters our eye 
we are at some distance in advance of the position 
we occupied when it started. During the 8 J min. 
the earth has moved in its orbit nearly 20J", so that 
(2) we never see that luminary in the place it occu- 
pies at the time of observation. 

Illustration. — Suppose a ball let fall from a point 
P, above the horizontal Kne A B, and a tube, of 
which A is the lower extremity, placed to receive it. 
If the tube were fixed, the ball would strike it on 
the lower side ; but if the tube were carried forward 
in the direction A B, with a velocity properly ad- 
justed at every instant to that of the ball, while pre- 
serving its inclination to the horizon, so that when 
the ball, in its natural descent, reached B, the tube 



136 



THE SOLAR SYSTEM. 



would liave been carried into tlie position BQ, it is 
evident that the ball throughout its whole descent 
would be found in the tube ; and a spectator refer- 
ring to the tube the motion of the ball, and carried 




ABERRATION OF LIGHT. 



along with the former, unconscious of its motion, 
would fancy that the ball had been moving in an 
inclined direction, and had come from Q. A very 
common illustration may be seen almost any rainy 
day. Choose a time when the air is still and the 
drops large. Then, if you stand still, you will -see 
that the drops fall vertically ; but if you walk for- 
ward, you will see the drops fall as if they were 
meeting you. If, however, you walk backward, you 
will observe that the drops fall as if they were com- 
ing from behind you. "We thus see that the drops 
have an apparent as well as real motion. 



THE EAETH. 



137 



The general effect of aberration of light is to cause 
each star to apparently describe a minute elhpse in 
the course of a year, the central point of which is 
the place the star would actually occupy were our 
globe at rest. 

Parallax. — This is the difference in the direction of 
an object as seen from tivo different places. For a 
simple illustration of it, hold your linger before you 




in front of the window. Upon looking at it with 
the left eye only, you will locate your linger at some 
point on the window ; on looking with the right eye 
only, you will locate it at an entirely different point. 
Use your eyes alternately and quickly, and you will 



138 THE SOLAR SYSTEM. 

be astonislied at the rate with which your finger 
will seem to change its place. Now, the difference 
in the direction of your finger as seen from the two 
eyes is parallax. 

In astronomical calculations, the position of a 
body as seen from the earth's surface is called its 
apparent place, while that in which it would be seen 
from the centre of the earth is called its true 
place. Thus, in the cut, a star is seen by the ob- 
server at O in the direction OP ; if it could be 
viewed from the centre R, its direction would be 
in the line RQ. It is therefore seen from O at a 
point in the heavens helow its position in reference 
to E. From looking at the cut, we can see (1), that 
the parallax of a star near the horizon is greatest, 
while it decreases gradually until it disappears alto- 
gether at the zenith, since an observer at O, as well 
as one at E, would see the star Z directly overhead ; 
and (2), that the nearer a body is to the earth the 
greater its parallax becomes. It has been agreed 
by astronomers, for the sake of uniformity in their 
calculations, to correct all observations so as to refer 
them to their true places as seen from the centre of 
the earth. Tables of parallax are constructed for 
this purpose. The question of parallax is also one 
of very great importance, because as soon as the 
parallax of a body is once accurately known, its dis- 
tance, diameter, etc., can be readily determined. (See 
Celestial Measurements.) 

Horizontal Parallax. — This is the parallax of 



THE MOON. 189 

a body when at the horizon. It is, in fact, the 
earth's semi-diameter as seen from the body. In the 
figure, the parallax of the star S is the angle OSR, 
which is measured by the line OE — the semi-diam- 
eter of the earth. The sun's horizontal parallax 
(8.94") is the angle subtended (measured) by the 
earth's semi-diameter as seen from that luminary. 
As the moon is nearest the earth, its horizontal par- 
allax is the greatest of any of the heavenly bodies. 

Annual Parallax. — The fixed stars are so distant 
from the earth that they exhibit no change of place 
when seen from different parts of the earth. The 
lines OS and ES are so long that they are ap- 
parently parallel, and it becomes impossible to 
discover the shghtest inclination. Astronomers, 
therefore, instead of taking the earth's semi-diam- 
eter, or 4,000 miles, as the measuring tape, have 
adopted the plan of observing the position of the 
fixed stars at opposite points in the earth's orbit. 
This gives a change in place of 183,000,000 miles. 
The variation of position which the stars under- 
go at these remote points is called their annual 
parallax, 

THE MOON. 

New Moon, ®. First Quarter, ®, Full Moon, ©. Last Quarter, ®. 

Its Motion in Space. — The orbit of the moon, con- 
sidering the earth as fixed, is an ellipse of which our 
planet occupies one of the foci. Its distance fi'om 



140 



THE SOLAE SYSTEM. 



the eartii, therefore, varies incessantly. At perigee 
it is 26,000 miles nearer than in apogee : the mean 
distance is about 238,000 miles. It would require a 
chain of thhty globes equal in size to the earth to 
reach the moon. An express-train would take about 
a year to accomplish the journey. The moon com- 
pletes its revolution (sidereal) around the earth in 
about 27^ days ; but, as the earth is constantly pass- 




PATH OF MOON. 



ing on in its own orbit around the sun, it requu^es 
over two days longer before it comes into the same 
position with respect to the sun and earth, thus com- 
pleting its synodic revolution. 



THE MOON. 141 

The real path of the moon is the result of its own 
proper motion and the onward movement of the 
earth. The two combined produce a wave-hke 
curve that crosses the earth's path twice each 
month ; this, owing to its small diameter com- 
pared with that of the ecliptic, is always concave 
toward the sun. As the moon constantly keeps 
the same side turned toward us, it follows that 
it must turn on its axis once each month. 

Dimensions. — Its diameter is about 2,160 miles. 
It would require fifty globes the size of the moon to 
equal the earth. Its apparent size varies with its 
distance ; the mean is, however, about one half a 



Fig. 41. 




THE SIZE OF MOON AT HORIZON AND ZENITH. 

degree, the same as that of the sun. It always ap- 
pears larger than it really is, on account of its 
brightness. This is the effect of what is termed in 
optics Irradiation. To illustrate this principle, cut 
two circular pieces of the same size, one of blact 



142 THE SOLAE SYSTEM. 

and the other of white paper. The white circle, 
when held in a bright light, will appear much larger 
than the black one. For the same reason it is often 
noticed that the crescent moon seems to be a part of 
a larger circle than the rest of the moon. As we 
have already said, the moon appears larger on the ho- 
rizon than when high up in the sky. By an examina- 
tion of the cut, it is easily seen that it is 4,000 miles 
nearer when on the zenith than when at the horizon. 
Besides these general variations in size, the moon 
varies in apparent size to different observers. Much 
amusement may be had in a large party or class by 
a comparison of its apparent magnitude. The esti- 
mates will differ from a small saucer to a wash-tub. 

LiBRATiONS {Uhrans, swinging). — ^While the moon 
presents the same hemisphere to us, there are three 
causes which enable us to see about 576 out of the 
1,000 parts of its entire surface. (1.) The axis of 
the moon is inclined a little to its orbit, as also its 
orbit is inclined to the earth's orbit; so when its 
north pole leans alternately toward and. from the 
earth, we see sometimes past its north, and some- 
times past its south pole. This is called lihration in 
latitude. (2.) The moon's rotation on its axis is al- 
ways performed in the same time, while its move- 
ment along its orbit is variable ; hence it happens 
that we occasionally see a httle further around each 
Umh (outer edge) than at other times. This is called 
lihration in longitude. (3.) The size of the earth is 
so much greater than that of the moon, that an ob- 



THE MOON. 143 

server, bj changing his position, can perceive dif- 
ferent portions of its surface near the limbs. 

Light and Heat. — If the whole sky were covered 
with full moons, they would scarcely make daylight, 
since its brilliancy cannot exceed ■3ot,Voo" that of the 
sun, while some authorities estimate it at less than 
half that amoimt. The moon's surface is supposed 
to be highly heated, possibly to the degree of boil- 
ing water, yet its rays impart no heat to us ; indeed 
Prof. Tyndall considers them rays of cold. This is 
probably caused by the fact that our dense atmos- 
phere absorbs all the heat, which in the higher re- 
gions produces the effect of scattering the clouds. 
It is a well-known fact that the nights are oftenest 
clear at full moon. 

Centke of Gravity. — It is thought that the centre 
of gravity of the moon is not exactly at its centre 
of magnitude, but nearly thirty-three miles beyond, 
and that the lighter haK is toward us. If that be 
so, this side is equivalent to a mountain of that 
enormous height. We can easily see that if water 
and air exist upon the moon, they cannot remain on 
this hemisphere, but must be confined to the side 
which is forever hidden from our view. 

Atmospheee of the Moon. — The existence of an 
atmosphere upon our satellite is at present an open 
question. If there be any, it must be extremely 
rarefied, perhaps as much so as that which is found 
in the vacuum obtained in the receiver of our best 
air-pumps. 



144 



THE SOLAR SYSTEM. 



Appearance of the Earth to Lunarians. — If there 
be any lunar inhabitants on the side toward ns, the 
earth must present to them all the phases which 
their world exhibits to us, only in a reverse order. 
When we have a new moon, they have a full earth, 
a bright fuU-orbed 

^ , Fig. 42. 

moon fourteen times 
as large as ours. The 
lunar inhabitants upon 
the side opposite to us 
of course never see our 
earth, unless they take 
a journey to the re- 
gions from whence it 
is visible, to behold 
this wonderful spec- 
tacle. Those living 
near the limbs of the disk might, however, on ac- 
count of the lihrations, get occasional glimpses of it 
near their horizon. 

The Earth-shine. — For a few days before and 
after new moon, we may distinguish the outHne of 
the unillumined portion of the moon. In England, 
it is popularly known as " the old moon in the new 
moon's arms." This reflection of the earth's rays 
must serve to keep the lunar nights quite light, 
even in neiv earth. 

Phases op the Moon.— The phases of the moon 
show conclusively that it is a dark body, which 
shines only bv reflecting the light it receives from 




APPEAKANCE OF EARTH AS SEEN yROM 
MOON. 



THE MOON. 



145 



tlie sun. Let us compare its various appearances 
with the positions indicated in the figure. 



Fig. 43. 




PHASES OF MOON. 



We see it (1) as a delicate crescent in the west 
just after sunset, as it first emerges from the sun's 



146 THE SOLAE SYSTEM. 

rajs at conjunction. It soon sets below tlie lioiizon. 
Half of its surface is illumined, but only a slendei 
edge with its horns turned from the sun is visible to 
us. Each night the crescent broadens, the moon 
recedes about 13° further from the sun, and sets cor- 
respondingly later, until at quadrature haK of the 
enlightened hemisphere is turned toward us, and the 
moon is said to be in her first quarter. Continuing 
her eastern progress round the earth, the moon (2) 
becomes gibbous^ in form, and, about the fifteenth 
day fi'om new moon, reaches the point in the heavens 
directly opposite to that ^\hich the sun occupies. 
She is then in opposition, the whole of the illumined 
side is turned toward us, and we have a full moon. 
She is on the meridian at midnight, and so rises in 
the east as the sun sets in the west, and vice versa. 

The moon (3) passing on in her orbit from oppo- 
sition, presents the same appearance as in her second 
quarter. The proportion of the illumined side visi- 
ble to us gradually decreases ; she becomes gibbous 
again ; rises nearly an hour later each evening, and 
in the morning lingers high in the western sky after 
sunrise. She now comes into quadrature, and is in 
her third quarter. 

From the thu'd quarter the moon (4) turns her en- 
lightened side from us and decreases to the crescent 
form again; as, however, the bright hemisphere 



* Gibbous means less than a half and mo]'e than a quartet 
cii-cle. 



THE MOON. 147 

constantly faces the sun, the horns are pointed 
toward the west. She is now seen as a bright cres- 
cent in the eastern sky just before sunrise. At last 
the illumined side is completely turned from us, and 
the moon herself, coming into conjunction with the 
sun, is lost in his rays. To accomplish this journej' 
through her orbit from new moon to new moon, has 
required 29J days — a lunar month. 

Moon runs high or low. — All have, doubtless, no- 
ticed that, in the long nights of winter, the full moon 
is high in the heavens, and continues a long time 
above the horizon ; while in midsummer it is low, 
and remains a much shorter time above the horizon. 
This is a wise provision of Providence, which is seen 
yet more clearly in the arctic regions. There the 
moon, during the long summer day of six months, is 
above the horizon only for her first and fourth quar- 
ters, when her light is least ; but during the tedious 
winter night of equal length, she is continually above 
the horizon for her second and third quarters. Thus 
in polar regions the moon is never full by day, but 
is always full every month in the night. We can 
easily understand these phenomena when we remem- 
ber that the new moon is in the same quarter and 
the full moon in the opposite quarter of the heavens 
from the sun. Consequently, the moon always be- 
comes fuU in the other solstice from that in which 
the sun is. When, therefore, the sun sinks very 
low in the southern sky the fuU moon rises high, 
and when the sun rises high the full moon sinks low. 



148 THE SOLAR SYSTEM. 

Haevest Moon. — ^Tiile tiie moon rises on the 
average 50 m. later eacli night, the exact time va- 
ries from less than half an hour to a fTill hour. 
Near the time of autumnal equinox the moon, at 
her full, rises about sunset a number of nights in 
succession. This gives rise to a series of brilliant 
moonlight evenings. It is the time of harvest in 
England, and hence has received the name of the 
Harvest Moon. Its return is celebrated as a festi- 
val among the peasantry. In the following month 
(October) the same occurrence takes place, and it is 
then termed the Hunter's Moon. The cause of this 
phenomenon hes in the fact that the ecliptic is vari- 
ously inclined to the horizon at different seasons of 
the year. When the equinoxes are in the horizon, 
the echptic makes a very small angle with the hori- 
zon ; whereas when the solstitial points are in the 
horizon, the angle is far gTeater. In the former 
case, the moon moving along the ecliptic, at the 
rate of 13° per day, will descend but little below the 
horizon in moving through many degrees, and so 
will come to view much earlier the ensuing night. 
This is the case when the sun is in Libra, and the 
moon consequently in the opposite sign, Aries. The 
least possible variation in the hour of rising is 17 
minutes — the gTeatest is 1 hour, 16 min. 

In the figure, S represents the sun, E the earth, 
M the moon ; C E the moon's path around the earth 
when the solstitial points are in the horizon — E D 
when the equinoxes are in the horizon ; 



THE MOON. 



149 



Fiff. 44. 



horizon; Mc? = M6 =13°, the distance the moon 
moves each day. When passing along the path C F, 
the moon sinks below the horizon the distance a b. 
and when mov- 
ing along the e^ 
path E D, only 
the distance 
cd. It is ob- 
vious that be- 
fore the moon 
can rise in the 
former case, 
the horizon 
must be de- 
pressed the 
distance a h, 
and in the lat- 
ter only cd; and the moon will rise correspondingly 
later in the one and earlier in the other. 

Nodes. — The orbit of the moon is inclined to the 
ecliptic about 5°, the points where her path crosses 
it being termed nodes. The ascending node (ft) is 
the place where the moon crosses in coming above 
the ecliptic or toward the north star ; the descending 
node ( y ) is where it passes below the ecliptic. The 
imaginary line connecting these two points is called 
the " line of the nodes." 

OccuLTATiON. — The moon, in the course of her 
monthly journey round the earth, frequently passes 
in front of the stars or planets, which disappear on 




HABVEST MOON, 



150 THE SOLAR SYSTEM. 

one side of her disk and reappear on the other. 
This is termed an occultation, and is of practical use 
in determining the difference of longitude between 
various places on the earth. 

Lunar Seasons; Day and Night, etc. — As the 
moon's axis is so nearly perpendicular to her orbit, 
she cannot properly be said to have any change of 
seasons. During nearly fifteen of our days, the sun 
pours down its rays unmitigated by any atmosphere 
to temper them. To this long, torrid day succeeds a 
night of equal length and polar cold. How strange 
the lunar appearance would be to us ! The disk of 
the sun seems sharp and distinct. The sky is 
black and overspread with stars even at midday. 
There is no twilight, for the sun bursts instantly 
into day, and after a fortnight's glare, as suddenly 
gives place to night; no air to conduct sound, no 
clouds, no winds, no rainbow, no blue sky, no gor- 
geous tintiDg of the heavens at sunrise and sunset, 
no delicate shadiag, no soft blending of colors, but 
only sharp outlines of sun and shade. 

What a bleak waste ! A barren, voiceless desert ! 
The nights, however, of the visible hemisphere must 
be brilliantly illuminated by the earth, while its 
phases " serve well as a clock — a dial all but fixed 
in the same part of the heavens, hke an immense 
lamp, behind w^hich the stars slowly defile along the 
black sky." 

Telescopic Features. — The lunar landscape is 
yet more wonderful than its other physical features 




1 I VNDSrAPF OF TIIK MOON 



152 THE SOLAR SYSTEM. 

Even with the naked eye we see on its surface bright 
spots — the summits of lofty mountains, gilded by 
the first rays of the sun — and darker portions, low 
plains yet lying in comparative shadow. The tele- 
scope reveals to us a region torn and shattered by 
fearful, though now extinct"^ volcanic action. Every- 
where the crust is pierced by craters, whose irregu- 
lar edges and rents testify to the convulsions our 
satellite has undergone at some past time. 

Mountains. — The heights of more than 1,000 of 
these lunar mountains have been measured, some of 
which exceed 20,000 feet. The shadows of the' 
mountains, as the sun's rays strike them obliquely, 
are as distinctly perceived tis that of an upiight 
staff when placed opposite the sun. Some of these 
are insulated peaks that shoot up solitary and alone 
from the centre of circular plains ; others are moun- 
tain ranges extending hundreds of miles. Most of 
the lunar elevations have received names of men 
distinguished in science. Thus we find Plato, Aris- 
tarchus, Copernicus, Kepler, and Newton, associated 
however with the Apennines, Carpathians, etc. 

Gray plains or seas. — These are analogous to our 
prairies. They were formerly supposed to be sheets 
of water, but have more recently been found to ex- 



* Several distinguished astronomers assert, however, that the 
crater Linnaeus has undergone of late certain marked changes. 
Its sides seem to have fallen in, and the interior to have become 
filled up, as if by a new eruption. It is said to present an ap 
pearance similar to that of the Sea of Serenity. 




TELE^COIXC MKW OF THE MOON 



154 THE SOLAR SYSTEM. 

hibit the uneven appearances of a plain, instead of 
the regular curve of bodies of water. The former 
names have been retained, and we find on lunar 
maps the " Sea of Tranquillity," the " Sea of Nec- 
tar," " Sea of Serenity," etc. 

Rills, luminous hands. — The latter are long bright 
streaks, irregular in outline and extent, which radi- 
ate in every direction from Tycho, Kepler, and other 
mountains ; the former are similar, but are sunken, 
and have sloping sides, and were at first thought to 
be ancient river-beds. Their exact nature is yet a 
mystery. 

Craters. — These constitute by far the most curious 
feature of the lunar landscape. They are of volcanic 
origin, and usually consist of a cup-like basin, with a 
conical elevation in the centre. Some of the craters 
have a diameter of over 100 miles. They are great 
walled j)lains, sunk so far behind huge volcanic ram- 
parts, that the lofty wall which surrounds an ob- 
server at the centre would be beyond his horizon. 
Other craters are deep and narrow, — as Newton, 
which is said to be about four miles in depth, — 
so that neither earth nor sun is ever visible from a 
great part of the bottom. The appearance of these 
craters is strikingly shown in the accompanying 
view of the region to the southeast of Tycho. (Fig. 
46.) 



ECLIPSES. 



155 



ECLIPSES. 

Eclipse of the Sun. — If the moon should pass 
through either node at or near the time of conjunc- 
tion or new moon, she would necessarily come be- 
tween the earth and the sun, for the three bodies 
are then in the same straight line. This would cause 



Fig. 47. 



ofete 



Sun 




ECLIPSE OF SUN. 



an eclipse of the sun. If the moon's orbit were in 
the same plane as the ecliptic, an eclipse of the sun 
would occur at every new moon ; but as the orbit is 
incHned, it can occur only at or near a node. 

The eclipse may he partial, total, or annular. — In 
Fig. 48, we see where the dark shadow (umbra) of 

Fig. 48 




UMBRA AND PENUMBRA. 



the moon faUs on the earth and obscures the entire 
body of the sun. To the persons within that region 



156 THE SOLAR SYSTEM. 

there is a total eclipse; the breadth of this space 
is not large, averaging only 140 miles. Beyond 
this umbra there is a lighter shado"^", penumbra 
(peiie, almost — imibra, a shadow), where only a 
portion of the sun's disk is obscured. "Within this 
region there is a ^jar^za^ eclipse. To those persons 
Living north of the umbra the echpse seems to pass 
over the lower limb of the sun ; to those south of the 
umbra it seems to pass over the upper limb. T\Tien 
the eclipse occurs exactly at the node, it is said to 
be central. If the eclipse takes place when the moon 
is at apogee, or furthest from the earth, her apparent 
diameter is less than that of the sun ; as a conse- 
quence, her disk does not cover the disk of the sun, 
and the visible portions of that luminary appear in 
the form of a ring (annulus) ; hence there is an an- 
nular eclipse in all those places comprised within the 
limits of the cone of shadow prolonged to the earth. 

General facts concerning a solar eclipse. — The fol- 
lowing data may perhaps guide in better under- 
standing the phenomena of solar eclipses. 

(1.) The moon must be new. 

(2.) She must be at or near a node. 

(3.) When her distance from the earth is less than 
the length of her shadow, the eclipse will be total 
or j)artial. 

(4.) When her distance is gTeater than the length 
of her shadow, the eclipse will be annular. 

(5.) There can be no eclipse at those places where 
the sun himself is invisible during the time. 



ECLIPSES. 



157 



(6.) An eclipse is not visible over the whole illu- 
mined side of the earth. As the moon's diameter 
is so much less than that of the earth, her cone of 
shadow is too small to enshroud the entire globe, so 
that the region in which it is visible cannot exceed 
180 miles in breadth. As, however, the earth is con- 
stantly revolving on its axis during the duration of 
the eclipse, the shadow may travel over a large sur- 
face of territory. 

(7.) If the moon's shadow faU upon the earth 
when she is just nearing her ascending node, it will 



Fig. 49 







SOLAR ECLIPTIC LIMIT (17°). 

only sweep across the south polar regions : if when 
nearing her descending node, it will graze the earth 
near the north pole. The nearer a node the con- 
junction occurs, the nearer the equatorial regions 
the shadow will strike. 

(8.) At the equator, the longest possible duration 
of a total solar eclipse is only about six minutes, and 
of an annular, twelve minutes. One reason of the 
greater length of the latter is, that then the moon 
is in apogee, when it always moves slower than 
when in perigee. The duration of total obscuration 
is greatest when the moon is in perigee and the sun 
in apogee ; for then the apparent size of the moon 
is greatest and that of the sun least. We see fi'om 



158 



THE SOLAE SYSTEM. 



this that the relative situation of the moon and sun 
decides the length and kind of the eclipse. 

(9.) There cannot be more than five nor less 
than two solar eclipses per year, and of these a total 
or an annular one is exceedingly rare. For instance, 
there has not been a total eclipse visible at London 
since 1715, and previous to that, there had been 
none visible for five and a haK centuries. 

(10.) A solar echpse comes on the western limb 
or edge of the sun and passes off on the eastern. 

(11.) The disk of the sun and moon is divided into 
twelve digits, and the amount of the echpse is esti- 
mated by the number of digits which it covers. Thus 
an ecHpse of six digits is one in which half the disk 
is concealed. 

Curious phenomena. — Various singular appearances 
sometimes attend a total eclipse. Around the sun is 
seen a beautiful Fig. 5o. 

corona or halo 
of hght, like 
that which paint- 
ers give to the 
head of the 
Virgin Mary. 
Flames of a 
blood-red color 
play around the 
disk of the moon, 
and when only 
a mere crescent 
of the sun is i!ni.TPf»! or isss 




ECLIPSES. 



159 



Fig. 51. 



visible, it seems to resolve itself into bright spots 
interspersed with dark spaces, having the appear- 
ance of a string 
of bright beads 
(Bailey's Beads.) 
Attendant cir- 
cumstances of a 
total eclipse. — 
These are of a 
peculiarly im- 
pressive charac- 
ter. The dark- 
ness is so intense 
that the brighter 
stars and planets 
are seen, birds 
cease their songs 
and fly to their nests, flowers close, and the face of 
nature assumes an unearthly cadaverous hue, while 
a sudden fall of the temperature causes the air to 
feel damp, and the grass wet as if from excessive 
dew. Orange, yellow, and copper tints give every 
object a strange appearance, and startle even the 
most indifferent. The ancients regarded a total 
eclipse with feelings of indescribable terror, as an 
indication of the anger of an offended Deity, or the 
presage of some impending calamity. Even now, 
when the causes are fully understood, and the time 
of the eclipse can be predicted within the fi-action 
of a second, the change from broad dayhght to in- 




ANNULAR ECLIPSE OP 183B SHOWINO BAILET'S 
BEADS. 



160 THE SOLAE SYSTEM. 

stantaneous gloom is overwhelming, and inspii'es 
with awe even the most careless observer. 

Curious custom among the Hindoos. — Among the 
Hindoos a singular custom is said to exist. When, 
during a solar ecHpse, the black disk of our satelhte 
begins slowly to advance over the sun, the natives 
believe that some terrific monster is gradually de- 
vouring it. Thereupon they beat gongs, and rend 
the air with most discordant screams of terror and 
shouts of vengeance. For a time their frantic efforts 
seem futUe and the ecUpse still progresses. At 
length, however, the increasing uproar reaches the 
voracious monster ; he appears to pause, and then, 
like a fish rejecting a nearly swallowed bait, grad- 
ually disgorges the fiery mouthful. When the sun 
is quite clear of the great dragon's mouth, a shout 
of joy is raised, and the poor natives disperse, ex- 
tremely self-satisfied on account of having so suc- 
cessfully relieved their deity from his late peril. 

The Sakos. — The nodes of the moon's orbit are 
constantly moving backward. They complete a rev- 
olution around the ecliptic in about eighteen and 
a half years. Now the moon makes 223 synodic 
revolutions in 18 yr. 10 da. ; the sun makes 19 rev- 
olutions with regard to the lunar nodes in about the 
same time. Hence, in that period the sun and 
moon and the nodes will be in nearly the same rela- 
tive position. If, then, we reckon 18 yr. 10 da. from 
any eclipse, we shall find the time of its repetition. 
This method was discovered, it is said, by the Chal- 



ECLIPSES. 161 

deaus. The ancients were enabled, by means of it, 
to predict eclipses, but it is considered too rough by 
modem astronomers : eclipses are now foretold cen- 
turies in advance, true to a second. In this manner 
historical incidents are verified, and their exact dates 
determined. 

Metonic Cycle. — The Metonic Cycle (sometimes 
confounded with the Saros) was not used for foretell- 
ing eclipses, but for the purpose of ascertaining the 
age of the moon at any given period. It consists of 
nineteen tropical years,"^ during which time there 
are exactly 235 new moons ; so that, at the end of 
this period, the new moons will recur at seasons of 
the year exactly corresponding to those of the pre- 
ceding cycle. By registering, therefore, the exact 
days of any cycle at which the new or full moons 
occur, such a calendar shows on what days these 
events will occur in succeeding cycles. Since the 
regulation of games, feasts, and fasts has been 
made very extensively, both in ancient and modern 
times, according to new or full moons, such a calen- 
dar becomes very convenient for finding the day on 
which the new or full moon required takes place. 
Thus if a festival were decreed to be held in any 
given year on the day of the first full moon after 
the vernal equinox : find what year it is of the 
lunar cycle, then refer to the corresponding year of 



* A tropical year is the interval between two successive returns 
of the sun to the venial equinox. 



162 



THE SOLAR SYSTEM. 



the preceding cycle, and the day will be the same as 
it was then. The Golden Number, a term still used 
in our almanacs, denotes the year of the lunar circle. 
Seven is the golden number for 1868. 

Eclipse of the Moon. — This is caused by the 
passing of the moon into the shadow of the earth, 

Fig. 52. 




ECLIPSE or THE MOON. 



and hence can take place only at full moon — oppo- 
sition. As the moon's orbit is inclined to the ecliptic, 
her path is partly above and partly below the earth's 
shadow ; thus an eclipse of the moon can take place 
only at or near one of the nodes. In the figure, the 
umbra is represented by the space between the lines 
K c and I h ; outside of this is the penumbra, where the 
earth cuts off the Hght of only a portion of the sun. The 
moon enters the penumbra of the earth at a, — this is 
termed her first contact with the penumbra ; next she 
encounters the dark shadow of the earth at b, — this is 
called ih.e first contact with the umbra ; she then emerges 
from the umbra at c, — ^which is called the second con- 
tact with the umbra ; finally, she touches the outer 
edge of the penumbra at d, — the second contact with the 
penumbra. Since the earth is so much larger than 



ECLIPSES. 163 

the moon, tlie eclipse can never be annular ; as, 
however, the eclipse may occur a little above or be- 
low the node, the moon may only partly enter the 
earth's shadow, either on its upper or lower limb. 
From the first to last contact with the penumbra, 
^YQ hours and a half may elapse. Total eclipses of 
the moon are rarer events than those of the sun, 
since the lunar ecliptic limit is only about 12° ; yet 
they are more frequently seen by us, (1) because each 
one is visible over the entire unillumined hemisphere 
of the earth, and also (2) because by the diurnal ro- 
tation during the long duration of the eclipse, large 
areas may be brought within its limits. So it will 
happen that while the inhabitants of one district wit- 
ness the eclipse throughout its continuance, those of 
other regions merely see its beginning, and others 
only its termination. The moon does not always 
completely disappear in total eclipses. The cause of 
this fact lies in the refraction of the solar rays in 
traversing the lower strata of the earth's atmos- 
phere ; they are analyzed, and purple our moon with 
the tints of sunset. The amount of refraction and 
the color depend upon the state of the air at the 
time. 

HiSTOKicAL Accounts of Eclipses. — The earliest 
account of an ecHpse on record is in the Chinese 
annals ; it is thought to be the solar eclipse of Octo- 
ber 13, 2127 B. c. On May 28, 584 b. c, one oc- 
curred which was predicted by Thales, as we have 
before mentioned. In the writings of the early Eng- 



164 THE SOLAR SYSTEM. 

lish cbroniclers are numerous passages relating to 
eclipses. William of Malmesbury thus refers to that 
of August 2, 1133, which was considered a presage 
of calamity to Henry I. : " The elements manifested 
their sorrows at this great man's last departure. 
For the sun on that day, at the 6th hour, shrouded 
his glorious face, as the poets say, in hideous 
darkness, agitating the hearts of men by an eclipse ; 
and on the 6th day of the week, early in the morn- 
ing, there was so great an earthquake, that the 
ground appeared absolutely to sink down ; an horrid 
noise being first heard beneath the surface." The 
same writer, speakiQg of the total eclipse of March 
20, 1140, says : " During this year, in Lent, on the 
13th of the kalends of April, at the 9th hour of the 
4th day of the week, there was an eclipse, through- 
out England, as I have heard. With us, indeed, and 
with all our neighbours, the obscuration of the Sun 
also was so remarkable, that persons sitting at table, 
as it then happened almost every where, for it was 
Lent, at first feared that Chaos was come again : 
afterwards learning the cause, they went out and 
beheld the stars around the Sun. It was thought 
and said by many, not untruly, that the king [Ste- 
phen] would not continue a year in the govern- 
ment." Columbus made use of an eclipse of the 
moon, which took place March 1, 1504, to reheve his 
fleet, which was in great distress from want of sup- 
plies. As a punishment to the islanders of Jamaica, 
who refused to assist him, he threatened to deprive 



THE TIDES. 165 

them of the light of the moon. At first they were 
indifferent to his threats, but " when the echpse ac- 
tually commenced, the barbarians vied with each 
other in the production of the necessary supplies for 
the Spanish fleet." 

THE TIDES. • 

Desceiption. — Twice a day, at intervals of about 
twelve hours and twenty-five minutes, the water be- 
gins to set in from the ocean, beating the pebbles 
and the foot of the rocky shore, and dashing its 
spray high in air. For about six hours it climbs 
far up on the beach, flooding the low lands and 
transforming simple creeks into respectable rivers. 
The instant of liigli-ivater or Jlood-tide being reached, 
it begins to descend, and the ebb succeeds the Jlow. 
The water, however, falls somewhat slower than it 
rose. 

Cause of the Tides. — The tides are caused by a 
great wave, which, raised by the moon's attraction. 

Fig. 58. 





Spring Tides 



SPRING TIDE, 

follows her in her course around the earth. The 
sun, also, aids somewhat in producing this eftect; 
but as the moon is 400 times nearer the earth, her 



166 THE SOLAR SYSTEM. 

influence is far greater. As the waters are free to 
yield to tlie attraction of the moon, she draws them 
away from C and D and they become heaped up at 
A. The earth, being nearer the moon than the 
waters on the opposite side, is more strongly at- 
tracted, and so, being drawn away from them, they 
are left heaped up at B. As the result, high-water 
is produced at A by the water being pulled from the 
earth, and at B by the earth being pulled from the 
water. The influence of the moon is not instanta- 
neous, but requires a little time to produce its full 
efl'ect ; hence high-water does not occur at any place 
when the moon is on the meridian, but a few hours 
after. As the moon rises about fifty minutes later 
each day, there is a corresponding difference in the 
time of high-water. While, however, the lunar tide- 
wave thus lags about fifty minutes every day, the 
solar tide occurs uniformly at the same time. They 
therefore steadily separate from each other. At one 
time they coincide, and high-water is the sum of 
lunar and solar tides ; at other times, high-water of 
the solar tide and low-water of the lunar tide occur 
simultaneously, and high-water is the difference 
between the lunar and solar tides. 

We should bear in mind the philosophical truth, 
that the tide in the open sea does not consist of a 
progressive movement of the water itself, but only 
of the form of the wave. 

Causes that modify tJie tides. — At new and full moon 
(the syzygies) the sun acts with the moon (as in Fig. 



THE TIDES. 167 

53) in elevating the waters ; this produces the liighest 
or Spring tide. In quadrature (as in Fig. 5 i), the 
sun tends to diminish the height of the water : this is 
called Neap-tide. When the moon is in perigee her 
attraction is stronger ; hence the flood-tide is higher 
and the ebb-tide lower than at other times. This re- 

Fisr. 54. 




Neap Tid.ee 




NEAP-TIDE. 



mark applies also to the sun. The height of the tide 
also varies with the declination of the sun and moon, 
— the highest or equinoctial tides taking place at the 
equinoxes, if, when the sun is over the equator, the 
moon also happens to be very near it : ,the lowest 
occur at the solstices. The force and direction of 
the winds, the shape of the coast, and the depth of 
the sea wonderfully complicate the explanation of 
local tides. 

Height of the tide at different places. — In the open 
sea the tide is hardly noticeable, the water some- 
times rising not higher than a foot ; but where the 
wave breaks on the shore, or is forced up into bays 
or narrow channels, it is very conspicuous. The 
difference between ebb and flood neap-tide at New 
York is over three feet, and that of spring tide over 



168 THE SOLAE SYSTEM. 

five feet ; while at Boston it is nearly double tliis 
amount. A headland jutting out into the ocean wlU 
diminish the tide ; as, for instance, off Cape Florida, 
where the average height is only one and a half feet. 
A deep bay opening up into the land hke a funnel, 
will converge the wave, as at the Bay of Fundy, 
wbere it rolls in, a great roaring wall of water sixty 
feet high, frequently overtaking and sweeping off 
men and animals. The tide sets up against the 
current of rivers, and often entirely changes their 
character ; for example, the Avon at Bristol is a 
mere shallow ditch, but at flood-tide it becomes a 
deep channel navigable by the largest Indiamen. 

Differential effect. — The whole attraction of the 
moon is only -^^-^ that of the sun : yet her influence in 
producing the tides and precession is greater, because 
that depends not upon the entire attraction either 
exerts, but upon the difference between their attrac- 
tion upon the earth's centre and upon the earth's 
nearest surface. For the moon, on account of her 
nearness, the proportion of the distance of these 
parts is treble that of the sun, and hence her greater 
effect. 

MAES. 

The god of war. Sign, ^ , shield and spear. 

Description. — Passing outward in our survey of the 
solar system, we next meet with Mars. This is the 
first of the superior planets, and the one most like 
the earth. It appears to the naked eye as a bright 



MAES. 



169 



red star, rarely scintillating, and shining ^vitli a 
steady light, which distinguishes it from the fixed 
stars. Its ruddy appearance has led to its being 
celebrated among all nations. The Jews gave it the 
appellation of '' blazing," and it bore in other lan- 
guages a similar name. At conjunction its apparent 

Fio^. 55. 




DIAMETER OF MARS AT EXTREME, LEAST. AND MEAN DISTANCES. 



diameter is only about 4"; but once in two years it 
comes into opposition with the sun, when its diam- 
eter increases to 30". At intervals of Syr. 7 mo. 
this occurs when the planet is also in perihelion 
and perigee. Mars then shines with a brilliancy 
rivalling that of Jupiter himself. 

Motion in Space. — Mars revolves about the Sun 
at a mean distance of about 140,000,000 miles. Its 
orbit is sufficiently flattened to bring it at perihelion 
26,000,000 miles nearer that luminary than when in 
aphelion. Its motion varies in different portions of 
its orbit, but the average velocity is about fifteen 

8 



170 THE SOLAE SYSTEM. 

miles per second. Tlie Martial day is about 40 min. 
longer than ours, and the year contains about 668 
Martial days, equal to 687 terrestrial days (nearly 
two years). 

Distance fkom Eaeth. — When in opposition, the 
distance of Mars is (hke that of all the superior 
planets) the difference between the distance of tbe 
planet and that of the earth from the Sun : at con- 
junction it is the sum of these distances. If the 
orbits were circular, these distances would be the 
same at every re^'olution. The elliptical figure, how- 
ever, occasions much variation. Thus, if it is in 
perihelion while the earth is in aphelion, the dis- 
tance is 126,000,000 - 93,000,000 = 33,000,000 miles. 

Dimensions. — Its diameter is a little less than 
5,000 miles. Its volume is about J that of the earth, 
but as its density is only J, it follows that its mass 
is only ^ of the terrestrial mass. A stone let fall on 
its surface would faU not quite five feet the first 
second. It is somewhat flattened at the poles, and 
bulges at the equator Hke our globe. 

Seasons. — The light and heat of the sun at Mars 
are less than one half that which we enjoy. Its axis 
is inclined about 28.7°, therefore its zones and sea- 
sons do not differ materially from our own : its days, 
also, as we have seen, are of nearly the same length. 
Since, however, its year is equal to nearly two of 
our years, the seasons are lengthened in proportion. 
There must be a considerable difference between the 
temperature of its northern and southern hemi- 



2d:AKS. 



171 



spheres, as the former has its summer when 26,000,000 
miles further from the sun than the latter : an in- 
creased length of 76 days may, however, be suffi- 
cient compensation. It has an atmosphere like our 
own, loaded with clouds. Mars has no moon. Its 
nights, therefore, are dark. Our own earth and 
moon must present in its evening sky a very beauti- 
ful pair of planets, showing all the phases which 
Mercury and Yenus present to us, the two always 
remaining within one half the moon's apparent di- 
ameter of each other. 

Telescopic Features. — Under the telescope. Mars 
exhibits slight phases, but by no means to the same 

Fig. 56. 




VIEW OP MAB8. 



extent as the inferior planets. Its surface appears 
covered with dusky patches, which are believed to 
be continents : these are of a dull red hue. Other 



172 THE SOLAK SYSTEM. 

portions, of a greenisli tint, are considered to be 
bodies of water. The proportion of land to water 
on the earth is reversed in Mars. " Here every con- 
tinent is an island ; there every sea is a lake : but 
these, like our own continents, are chiefly confined to 
one hemisphere, so that the habitable area of the 
two globes may not differ so much as the size of the 
planets." The ruddy color of the planet is thought 
by Herschel to be due to an ochrey tinge in the 
soil ; by others it is attributed to peculiarities of the 
atmosphere and clouds. Lambert suggests that it 
is the color of the vegetation, which, on Mars, may 
be red instead of green. There are constant 
changes going on in the brightness of the disk, 
owing, it is supposed, to the variation of the clouds 
of vapor in its atmosphere. No mountains have yet 
been discovered. In the vicinity of the poles are 
brilliant white spots, which are considered to be 
masses of snow. The " snoiu zoiies' apparently melt 
and recede with the return of summer in each hemi- 
sphere, and increase on the approach of winter. We 
can thus from the earth watch the formation of polar 
ice and the fall of snow — in fact, all the vicissitudes 
of the seasons on the surface of a neighboring 
planet. 

THE MINOE PLANETS. 

DiscoYEEY. — Beyond Mars there is a wide interval 
which until the present century was not filled. The 
bold, imaginative Kepler conjectured that there was 



THE MINOR PLANETS. 



173 



a planet in this space. This supposition was cor- 
roborated by Titius's discovery of what has since 
been known as Bode's law. 

Take the numbers 0, 3, 6, 12, 24, 48, 96, 192, 384, 
each of which, after the second, is double the pre- 
ceding one. It' we add 4 to each of these numbers, 
we form a new series : 

4, 7, 10, 16, 28, 52, 100, 196, 388. 

At the time this law was discovered, these numbers 
represented very nearly the proportionate distance 
from the sun of the planets then known, taking the 
earth's distance as ten, except that there was a blank 
opposite 28.^ This naturally led to inquiry, and a 
systematic effort to solve the mystery. On the 1st 
day of January, 1801, the nineteenth century was 
inaugurated by Piazzi's discovery of the small 
planet Ceres, at almost the exact distance necessary 
to fill the gap in Bode's series. This was soon fol- 
lowed by the announcement of other new planets, 
until (1868) there are one hundred and one, and a 
probability of many more. Indeed, Leverrier has 
calculated that there may be perhaps 150,000 in all. 



* PT.AiTETS. 


True dis- 
tance 
from o. 


Distance 

by Bode's 

law. 


PLANETS. 


True dis- 
tance 
from •. 


Distance 

by Bode"a 

law 


Vulcan 

M ercury 

Venus 

Earth . 


3.87 
7.23 
10.00 
15.23 


4.00 
7.00 
10.00 
16.00 


Ceres 

Jupiter 

Saturn 

Uranus 

Neptune 


27.66 
52.03 
95.39 
191.82 
300.37 


28.00 
52.00 
100.00 
196.00 


Mars 


3SS.0O 







174 THE SOLAE SYSTEM. 

Desckiption. — These minor worlds, or " pocket 
planets," as Herschel styled them, are extremely 
diminutive. The largest of them is Pallas, whose 
diameter is perhaps 600 miles. Those recently dis- 
covered are so small that it is difficult to decide 
which is the smallest. A French astronomer recently 
remarked concerning them, that a "good walker 
could easily make the tour of one in a day;" a 
prairie farmer would need to pre-empt a whole one 
for a flourishing cornfield. They all revolve about 
the sun in regular orbits, comprising a zone about 
100,000,000 miles in width. Their paths are va- 
riously inclined to the ecliptic ; some coincide, while 
that of Pallas rises 34°. 

Okigin. — One theory concerning the origin of these 
small planets is, that they are the fragments of a 
large planet which, in a remote antiquity, has been 
shivered to pieces by some terrible catastrophe. 
" One fact seems above all others to confirm the 
idea of an intimate relation between these planets. 
It is this : if their orbits consisted of soHd rings, 
they would be found so entangled that it would be 
possible, by taking up any one at random, to Hft 
all the rest." Another theory is given under the 
" Nebular Hypothesis." 

Names and signs. — Ceres, the first discovered, re- 
ceived the symbol 9 , a sickle. This was appropri- 
ate, since that goddess was supposed to preside over 
harvests. Pallas, the second, named from the god- 
dess of wisdom and scientific warfare, obtained the 



JUPITEE. 175 

sign i , the head of a spear. To Juno, the third 
planet, was assigned o , a sceptre surmounted with 
a star, the emblem of the queen of heaven. An 
altar with fire upon it, S , appropriately represented 
Vesta, the household goddess, whose sacred fire was 
kept burning continually. In this way names of 
goddesses and appropriate symbols were used to 
designate the minor planets which were earliest dis- 
covered. Since then a simple circle with the num- 
ber inclosed has been adopted; thus ® represenvs 
Ceres — (D is the sign of Pallas. 



JUPITER. 

The king of the gods. Sign U, a hieroglyphic representation of an eagk 
"the bird of Jove." 

Description. — From the smallest members of thd 
solar system we now pass at once to the largest 
planet — the colossal Jupiter. Its peculiar splendor 
and brilliancy distinguish it from the fixed stars, 
and vie even with the lustre of Yenus. It is one of 
the five planets discovered in primitive ages. In 
those early times, Jupiter was supposed to be the 
cause of storm and tempest. Pliny thought that 
lightning owed its origin to this planet. An old al- 
manac of 1368, foretelling the harmless condition of 
Jupiter for a certain month, says, " Jubit es hote 
and moyste and does weel til al thynges and noyes 
nothing." 



176 THE SOLAK SYSTEM. 

Motion in Space. — Jupiter reyolves about the sun 
at a mean distance of 475,000,000 miles. His orbit 
has much less eccentricity than those of the smaller 
planets. Were his path very elliptical, the attrac- 
tion of the sun would be insufficient to bring him 
back from its extreme limit, and the huge un- 
wieldy planet would plunge headlong into space. 
This careful fitting, whereby the plan is always 
modified to accomphsh an end, is everywhere 
characteristic of nature, and is a continued rev- 
elation of its common Author. The revolution 
of Jupiter among the fixed stars is slow and ma- 
jestic, comporting well with his vast dimensions 
and the dignity conferred by four attendant worlds. 
He advances through the zodiac at the rate of one 
constellation yearly ; so that if we locate the planet 
now, a year hence we can find it equally advanced 
in the next sign. Yet slowly as he seems to travel 
through the heavens, he is bowling along through 
space at the enormous speed of 500 miles per min- 
ute. The Jovian day is only equal to about ten of 
our hours, while his year is lengthened to about 
12 of our years, comprising near 10,000 of his days. 

Distance feom Eaeth. — Once in thirteen months 
Jupiter is in opioosition, and his distance from the 
earth is measured by the difference of the distances 
of the two bodies from the sun. At the expn-a- 
tion of half this time he is in conjunction, and his 
distance from us is measured by the sum of these 
distances. 



JUPITEE. 



177 



Fiff. 57. 




Dimensions. — Its diameter is about 88,000 miles, 
or one-tenth of the sun. Its volume is 1,400 times 
that of the earth, 
and much exceeds 
th at of aU the other 
planets combined. 
Seen at the dis- 
tance of the moon, 
this immense 
globe would em- 
brace 1,200 times 
the space of the 
full moon. Jupi- 
ter's density is 
only one-fifth that 

of the earth ; moreover, its rapid rotation upon its 
axis, whereby a particle on the equator revolves 
with a velocity of 467 miles per minute against the 
earth's 17 miles per minute, must produce a power- 
ful centrifugal force which materially diminishes the 
weight of all objects upon its surface. Consequently 
a stone let fall on Jupiter would pass through but 
about thirty-nine feet the first second. As a result 
also of this rapid rotation, the planet is the most 
flattened of any in the solar system — the equatorial 
diameter exceeding the polar by about 5,000 miles. 

Seasons. — As the axis of Jupiter is but slightly 
inclined from a perpendicular to the plane of its 
orbit, there is but little difi^erence in the length of 
its days and nights, which are each of about five 



178 THE SOLAK SYSTEM. 

hours' duration. At the poles the sun is visible for 
nearly six years, and then remains set for the same 
length of time. The seasons also are but slightly 
varied. Summer reigns near the equator, while the 
temperate regions enjoy perpetual spring. The hght 
and heat of the sun are only 2V of that which we re- 
ceive; yet peculiarities of soil or atmosphere may 
compensate this difference. The evening sky on 
Jupiter must be inexpressibly magnificent; besides 
the glittering stars which adorn our heavens, four 
moons, waxing and waning, each with its diverse 
phase, illuminate its night. All the starry exhibition 
sweeps through the sky in five hours. 

Telescopic Features. — Jupiter s moons. — Under 
the telescope Jupiter presents a beautiful Copernican 
system in miniature. Four small stars — moons — are 
seen to accompany it in its twelve-yearly revolutions. 
From hour to hour their positions vary, and they 
seem to oscillate from one side to the other of the 
planet. At one time there will be two on each side, 
and again, three on one side ; while the remaining 
star is left alone. They are also frequently found 
to disappear, one, two, or even three at a time, and, 
more rarely, all four at once. There are well- 
authenticated instances on record of their ha"sdng 
been seen by the naked eye. Among others, the 
following singular case is mentioned. Wrangle, the 
celebrated Russian traveller, states, that when in Si- 
beria, he once met a hunter, who said, pointing to 
Jupiter, "I have just seen that star swallow a small 



JUPITER. 



179 



one and then vomit it up again." These moons are 
called by the ordinal numbers, reckoning outward 
from the planet. With an ordinary glass, there is 
nothing to distinguish them from small stars. The 
Illd, however, being the largest and brightest, will 
generally be identified easiest. The 1st satellite ap- 
pears to the inhabitants of the planet almost as 
large as our moon to us ; the lid and Illd about 
half as large. Their real size and density are in- 
dicated in the following table. It will be seen that 
the lYth is lighter than cork : 



Satellites of Jupiter. 



I. lo 

n. Enropa ... 
ni. Ganymede 
IV. Callisto..., 



Mean distance 
from Jupiter. 



267,380 

425,156 

678,393 

1,192,823 



Diameter. 



2,352 m. 
2,099 " 
3,436 " 
2,929 " 



Density. 
Water as 1. 



.114 
.171 



.222 



Sidereal period. 



7 3 
19 16 



18 28 
13 4 
3 43 



32 



It is noticeable that here are four satellites revolv- 
ing about Jupiter, one of them larger than the planet 
Mercury, and each far surpassing in size the minor 
planets between Mars and Jupiter. The moons are 
not only thus distinguished by their various dimen- 
sions, but also by the variety of their color. The 
1st and lid have a bluish tint, the Illd a yeUow, 
and the lYth a reddish shade. The total space oc- 
cupied by this miniature system is about two and 
a half million miles in diameter. 

Eclipse of the moons. — Jupiter, like all celestial bodies 
not self-luminous, casts into space a cone of shade. 



180 



THE SOLAR SYSTEM. 



The 1st, lid, and Illd satellites revolve in or- 
bits but very little inclined to the plane of the 
planet's orbit. During each revolution they pass 



Fig. 58. 





ECLIPSES AND OCCULTATIONS Or JUPITER'S MOONS. 

between the Sun and Jupiter, producing a solai 
ecHpse ; and also by passing through the shadow of 



JUPITEE. 181 

the planet itself, cause to themselves an eclipse of 
the sun, and to Jupiter an eclipse of a moon. The 
IVth passes through a path more inclined, and there- 
fore its eclipses are less frequent : instead of being 
fullj eclipsed, it sometimes just grazes the shadow, 
as it were, and so its Kght is much diminished. 
Through a telescope we can distinctly watch the 
disappearance or immersion of the satellites in the 
planet's shadow, their reappearance or emersion, and 
also their transits, as a round black dot or shadow 
moving across the disk of Jupiter. In the cut, we 
see represented the various positions of the moons : 
the 1st is eclipsed; the lid is passing across the 
disk of the planet on which its shadow is also thrown ; 
the Illd is just behind the planet, and so occulted or 
concealed, while it has not yet entered the bliadow ; 
the IVth is in view from the earth. These satellites 
revolve with great rapidity, as is necessary in order 
to overcome the superior attraction of the planet and 
prevent being drawn to its surface. The 1st goes 
through all its phases in 1| days, and the lYtli in less 
than twenty days. A spectator on Jupiter might 
witness, during the Jovian year, 4,500 eclipses of 
the moon (moons), and about the same number of 
the sun. 

Jupiter's belts. — These are dusky streaks of 
varying breadth and number, lying more or less 
parallel to the planet's equator, but terminating at a 
short distance from the edges of the disk. BetAveen 
these a brighter, often rose-colored space, marks the 



182 THE SOLAE SYSTEM. 

equatorial regions. They are not permanent, but 
change sometimes very materially in the course of 
a few minutes. Occasionally only two or three 
broad belts are seen ; at other times a dozen narrow 
ones appear. It is supposed that the planet is en- 
veloped in dense masses of cloud, and that the belts 
are merely fissures, laying bare the solid body be- 
neath. The parallel appearance is doubtless due to 
strong equatorial currents, analogous to our trade- 
winds. 

Yelocity of Light. — By an attentive examination 
of the eclipses of Jupiter's moons, Romer (a Danish 
astronomer, in 1617) was led to discover the pro- 
gressive motion of light. Before him, it had been 
considered instantaneous. He noticed that the ob- 
served times of the eclipses were sometimes earlier 
and sometimes later than the calculated times, ac- 
cording as Jupiter was nearest or furthest from the 
earth. His investigations convinced him that it 
requires about 16 J min. for light to traverse the orbit 
of the earth. Romer's conclusion has since been 
verified by the phenomena of aberration of light. 
The velocity of light is about 183,000 miles per 
second. 

SATURN. 

The god of time. Sign ^ , an ancient scythe. 

Description. — We now reach, in our outward jour- 
ney from the sun, the most remote world known to 
the ancients. On accoimt of its distance, it shines 



SATUEN. 



183 



with a feeble but steady pale yellow light, which dis- 
tingnishes it from the fixed stars. Its orbit is so 
vast that its moyement among the constellations 
may be easily traced through one's lifetime. It re- 
quires two and a half years to pass through a single 
sign of the zodiac ; hence, when once known, it may 
be easily found again. The earth leaves it at con- 
junction, makes a yearly revolution about the sun, 
comes to its starting point, and overtakes Saturn in 
about thirteen days thereafter.* On account of its 
slow, dreary pace, Saturn was chosen by the ancients 
as the symbol for lead. It is smaller than Jupiter, 
but much more gorgeously attended. Besides a 
retinue of eight satellites, it is surrounded by a sys- 
tem of rings, some shining with a golden light and 
others transparent — a spectacle which is as wonder- 
ful as it is unique. 



Motion in 
Space. — Saturn 
revolves about 
the sun at a 
mean distance 
of 872,000,000 
miles. The 
eccentricity of 
its orbit is a 
trifle more than 
that of Jupiter, 



Fie. 59. 




* From this the year of Saturn may be determined. As 13 : 378 
days : : Earth's year : Saturn's year = 30 yr. nearly 



184 THE SOLAR SYSTEM. 

SO that while it may at perihelion come fifty mil- 
lion miles nearer than its mean distance, at aphe- 
lion it swings off as much beyond. We can form 
some estimate of the size of its immense orbit, 
when we remember that it is moving along at the 
rate of 21,000 miles per hour, and yet as we look 
at it from night to night, we can scarcely detect any 
change of place. The Saturnian year is equal to 
about thirty of ours, and comprises nearly 25,000 
Saturnian days, each of which is about ten and a 
liaK hours in length. 

Distance from Earth. — This is found in the same 
manner as that of the other superior planets, being- 
least in opposition and greatest at conjunction. As 
the earth and Saturn occupy different portions of 
their orbits, the distances between them at different 
times may vary 200,000,000 miles. 

Dimensions. — Its diameter is about 72,000 miles. 
Its volume is nearly 750 times that of the earth. Its 
density is very low indeed, being much less than that 
of water, and about the same as that of pine wood. 
The Saturnian force of gra-^dty is therefore scarcely 
greater than the terrestrial, so that a stone falls 
toward the surface of that immense globe only about 
seventeen feet the first second. 

Seasons. — The light and heat of the sun at Saturn 
are only y^ that which we receive. The axis of 
Saturn is inchned from a perpendicular to the 
plane of its orbit about 31°. The seasons there- 
fore are similar to those on the earth, but on a 



SATUEN. 185 

larger scale. The sun cKmbs in summer about 8° 
higher above the horizon, and sinks correspondingly 
lower in winter. The tropics are 16° further apart, 
and the arctic and antarctic circles 8° further from 
the poles. Each of Saturn's seasons lasts more than 
seven of our years. There is about fifteen years 
interval between the autumn and spring equinoxes, 
and between the summer and whiter solstices. For 
fifteen years the sun shines on the north pole, and a 
night of the same length envelops the south pole. 
The atmosphere is doubtless very dense, as the belts 
would seem to indicate. 

Telescopic Features. — Saturn's Rings. Galileo 
first noticed something pecuhar in the shape of Sat- 
urn. Through his imperfect telescope it seemed to 
have on each side a small planet like a supporter, 
to help old Saturn on his way. He therefore an- 
nounced to his friend Kepler his curious discovery, 
that "Saturn is threefold." As the planet, how- 
ever, approached its equinoxes, these attendants van- 
ished altogether from his simple instrument. This 
was a great perplexity to Galileo, and he never 
solved the mystery. When the rings were after- 
ward seen, their real form was not known. They 
were supposed to be a kind of handle attached to the 
planet, but for what purpose was not explained. 

The series consists of three rings of unequal 
breadth, surrounding the j)lanet at the equator. The 
exterior ring is separated from the middle one by a 
distinct break, while the interior one seems joined 



186 THE SOLAR SYSTEM. 

to the middle one. They differ in their brightness : 
the exterior ring is of a grayish tint ; the middle one 
is the most brilliant and is more luminous than Sat- 
urn itself ; the interior is dusky and has a purple 
tinge. The exterior and middle rings are both 
opaque and cast on the planet a distinct shadow ; 
while the interior one is so transparent that it ap- 
pears upon the globe of Saturn as a dark band 
through which the surface of the planet is readily 
seen. The dimensions of the rings are given in the 
following table (Guillemin) : 

Miles. 

Diameter of exterior ring 173,500 

Breadth of exterior ring 10,000 

Diameter of middle ring 150,000 

Breadth of middle ring 18,300 

Distance between exterior and middle ring 1,750 

Diameter of interior ring 113,400 

Breadth of interior ring 9,000 

Distaiice of interior ring from planet 10,150 

Entire breadth of ring system 39,050 

Thickness of rings not more than 100 

The rings revolve around Saturn in about lOJ 
hours, in the same direction as the planet revolves 
on its axis. The globe of Saturn is not exactly at 
the centre of the rings. This fact, combined with 
the rotary motion, is essential to the stability of the 
rings, preventing them from being precipitated in 
an overwhelming ruin and devastation upon the 
body of the planet. 

Phases of the rings. — The plane of the rings is in- 
clined 28° to the ecliptic. In its revolution about 
the &un, the axis of Saturn remaining parallel to 



SATURN. 187 

itself, the sun sometimes illumines the northern 
and sometimes the southern face of the rings. At 
Saturn's equinoxes the edge only receives the light, 
and the rings are invisible to us, except with the 

Fig. GO. 




PHASES OP SATURN'S RINGS. 

most powerful telescopes, and then only as a line of 
light. The body of the planet constantly cuts off 
the sun's rays from a portion of the rings, and also 
occasionally conceals from our view some of the lu- 
minous part. By a careful study of the cut these vari- 
ous positions of the planet and rings, with the most 
favorable times for observation, may be understood. 
Belts. — The surface of Saturn is traversed by dusky 
belts of a less distinct and definite appearance than 



188 THE SOIAR SYSTEM. 

those upon Jupiter. The equatorial regions are 
brighter than the other parts of the disk ; the poles 
especially are less luminous. 

Satellites. — Saturn has eight satellites, named — 

1. Mimas. 3. Tetbys. 5. Rhea. 7. Hypeiion. j 

2. Enceladus. 4 Dione. 6. Titan. 8. lapetus. 

lapetus is the largest of these, and in size exceeds 
Mars. Enceladus and Mimas are the faintest of 
t\\inklers, and can only be seen with a powerful 
telescope, and under most favorable circumstances. 
They were first detected by Herschel, "threading 
like pearls the silver line of light," to which the 
ringj then seen edgewise, was reduced, — advancing 
off it at either end, returning, and then hiding them- 
selves behind the planet. The first four of these 
moons are nearer to Saturn than our moon to the 
earth, but lapetus is nearly ten times as distant : so 
that the diameter of the Saturnian system is nearly 
four and a half million miles. The movements are 
extremely rapid. Mimas traverses a space equal to 
the diameter of our moon in two minutes, passing 
from new to full in twelve hours, — a little more than 
a Saturnian day. 

Satukotan Scenery. — The grandeur and mag-nifi- 
cence of the scenery upon Saturn undoubtedly far 
surpass anything with which we are familiar. In 
the cut is given an ideal view of a landscape located 
upon the planet at a latitude of about 28°, taken 
about midnight. The rings form an immense arch,. 



UEANUS. 



189 



which spans the sky and sheds a soft radiance 
around; while to add to the strange beauty of the 



Fig. 61. 




rOEAL LANDSCAPE ON SATURN. 



Saturnian night, eight moons in all their different 
phases, full, new, crescent, or gibbous, Hght up the 
starry vault. 

UKANUS. 

" Heaven," the most ancient of the gods. Sign Ijt ; H, the initial letter of 
Herschel, with a planet suspended from the cross-bar. 

Desckiption. — On the 13th of March, 1781, between 
10 and 11 p. M., Sir WiUiam Herschel was engaged 
in examining with his great telescope some stars 
in the constellation Gemini. One small star at- 
tracted his attention, which he accordingly observed 
with a higher magnifying power, when, unlike the 



190 THE SOLAR SYSTEM. 

effect produced on the fixed stars, its disk widened- 
Watching it for several nights, he detected its mo- 
tion in space, and, mistaking its true character, 
announced the discovery of a new comet. A few 
months' examination revealed the error, and the new 
body was universally admitted to be a member of 
the solar system — new to us, but older perhaps than 
our own world. It is now known that Uranus had 
been previously observed by other astronomers. 
Indeed, Le Monier at Paris had watched it for 
twelve successive nights, but pronounced it a fixed 
star. Since he had also seen it on previous occa- 
sions, had he been an orderly observer, he would 
doubtless have detected its planetary character ; but 
he was extremely careless, as may be inferred from 
the fact related by Arago, that he had been shown 
one of Le Monier's observations of this planet writ- 
ten on a paper bag which originally contained hair- 
powder purchased at a perfumer's. Uranus may be 
seen by a person of strong eyesight in a perfectly 
dark sky, if he previously knows its exact position 
among the stars. Its faintness is due to its great 
distance from the earth. Were it as near as the sun, 
it would appear twice as large as Jupiter. 

Motion in Space. — Uranus revolves about the sun 
at a mean distance of 1,754,000,000 miles. Its year 
exceeds eighty-four of ours. 

Dimensions. — Its diameter is about 33,000 miles. 
It is lighter than water, having a density about 
equal to that of ice. 



NEPTUNE. 191 

Seasons. — We know little of the seasons of Uranus. 
Since its axis lies in the plane of its orbit, the sun 
winds ill a spiral form around the whole planet. The 
light and heat are only y^Vo of that which we 
receive ; the light is about the quantity which would 
be afforded by three hundred full moons. The in- 
habitants of Uranus can see Saturn, and perhaps 
Jupiter, but none of the planets within the orbit 
of the latter. 

Telescopic Features. — No spots or belts have 
been discovered with any telescope yet made. The 
time of rotation and other features so familiar to us 
in the nearer planets, are unknown with regard to 
Uranus. 

Satellites. — Uranus has four moons, of which 
little is known except the curious fact that their 
orbits are nearly perpendicular to the plane of the 
planet's orbit, and that their movements are retro- 
grade — i. e., in the same direction as the hands of a 
watch. 

NEPTUNE. 

The god of the sea. Sign ]p, his trident. 

Desckiption. — ^Neptune is the far-off sentinel at 
the very outposts of the solar system, being the most 
distant planet of which we have any knowledge. It 
is invisible to the naked eye, and appears in the tel- 
escope as a star of the eighth magnitude. 

Discovery. — For many years the motions of Ura- 
Dus were such as to baffle the most perfect calcula- 



192 THE SOLAR SYSTEM. 

tions. While far-distant Saturn came around to his 
place true to the minute and second, even after his 
journey of nearly thirty years, Uranus defied arith- 
metic, and refused to conform to the time set down 
for him on the heavenly dial. 

At length it was suggested by several astronomers 
that there was another planet outside of its orbit, 
whose attraction produced these perturbations. So 
marked was this impression with Herschel, that he 
writes : " We see it as Columbus saw America from 
the shores of Spain. Its movements have been felt 
trembling along the far-reaching line of our analysis 
with a certainty not far inferior to ocular demonstra- 
tion." Finally, two young mathematicians, Lever- 
rier of Paris, and Adams of Cambridge, England, 
each unknow^n to the other, set themselves about the 
task of finding the place of this new planet. The 
problem was this : Given the disturbances produced 
hy the attraction of the unknown planet, to find its orbit 
and its ijlace in the orbit. Adams, after assiduous 
labor for nearly two years, completed his calcula- 
tions and submitted them to Prof. Airy, the Astron- 
omer Koyal, in October, 1845. In the summer of 
1846, Leverrier laid a paper before the Academy of 
Sciences in Paris, announcing the position of the 
unknown planet. Prof. Airy, hearing of this, was so 
impressed with the value of Adams's calculations, 
that he wrote to Prof. Challis, of Cambridge, to use 
his large telescope to search that quarter of the 
heavens. Prof. Challis did as requested, and saw a 



NEPTUNE. 193 

star which afterward proved to be the planet so 
anxiously sought for, although at that time he failed 
to ascertain its true character. On September 23d, 
of the same year, Leverrier wrote to Berlin, asking 
for assistance in searching for the planet. Dr. Galle, 
that same eyening, turned the large telescope of the 
Observatory to the place indicated, and almost im- 
mediately detected a bright star not laid down in 
the maps. This proved to be the predicted planet, 
found within less than a degree of the spot de- 
scribed by Leverrier. Such is the history of one of 
the grandest achievements of the human mind. It 
stands as an ever fresh and assuring proof of the 
exactness of astronomical calculations, and the pow- 
er of the intellect to understand the laws of the God 
of Nature. 

Motion in Space. — ^Neptune revolves about the 
sun at a mean distance of about 2,750,000,000 of 
miles. The Neptunian year is equal to nearly 165 
terrestrial ones. Its motion in its orbit is the slow- 
est of any of the planets, since it is the most remote 
from the sun. The velocity decreases from Mercury, 
which moves at the rate of 105,000 miles per hour, 
to Neptune, whose rate is only 12,000 miles. 

Dimensions.— Its diameter is about 37,000 miles. 
Its volume is nearly 100 times that of the earth. Its 
density is about that of Uranus, a little less than that 
of w^ater. 

Seasons. — As the inclination of its axis is un- 
known, nothing can be ascertained concerning its 



194 THE SOLAK SYSTEM. 

seasons. The sun gives to Neptiine but Yiho ^^^ 
light and heat which we receive. 

Though at the extreme of the solar system, 2,650 
millions of miles beyond us, the same heavens bend 
above, the same starry sky is seen by night — the 
Milky Way is no nearer to the eye, the fixed stars 
shine no more brightly. The planets, however, are 
all too near the sun to be seen, except Saturn and 
Uranus. The Neptunian astronomers, if there be 
any, are well situated for observing the orbits of 
comets, and for measuring the annual parallax of 
the stars, since they have an orbit of 5,500 million 
miles in diameter, and hence the angle must be 30 
times as great as that which the terrestrial orbit 
affords. 

Telescopic Features. — On account of the recent- 
ness of the discovery of this planet and its immense 
distance, nothing is known of its rotation or physical 
features. 

Satellites. — Neptune has one moon, at nearly the 
same distance from it as our o'^ti moon is from the 
earth. The revolution of this about the planet, 
which is accompHshed in about six days, has fur- 
nished the materials for calculating the mass of 
Neptune. 

METEOKS AND SHOOTING STAES. 

Desceiption. — All are familiar with those lumin- 
ous bodies that flash through our atmosphere as if 



METEOES AND SHOOTING STARS. 



195 



the stars were indeed falling from heaven. Differ- 
ent names have been applied to them, although tho 
distinction is not very definite. (1) Aerolites are those 



Fiff. 62. 




A METEOR WITH ITS TRAIN. 



stony masses which fall to the earth. (2) Shooting 
Stars are those evanescent brilliant points that sud- 



196 THE SOLAK SYSTEM. 

denly dart tlirongli tlie higher regions of the air, 
leaying a fiery train behind. (3) Meteors are kimin- 
ous bodies which have a sensible diameter and a 
spherical form. They frequently pass over a great 
extent of country, and are seen for some seconds of 
time. Many leave behind a train of glowing sparks i 
others explode with reports like the discharge of 
artillery, — the pieces either continuing their course, 
or falling to the earth as aerolites. Some meteors, 
doubtless, after having favored us with a transient 
illumination, pass on into space ; some are vapor- 
ized ; while others are burned and the ashes and 
fi'agments fall to the gi'ound. 

Aeeolites. — The fall of aerolites is frequently men- 
tioned and well authenticated. Chinese records tell 
of one as long ago as in 616 B. c, which, in its faU, 
broke several chariots and killed ten men. A block 
of stone, equal to a full wagon-load, fell in the Helles- 
pont, B. c. 465. By the ancients, these stones were 
held in great repute. The Emperor Jehangire, it is 
related, had a sword forged from a mass of meteoric 
iron which fell in the Punjab in 1620. In 1795, a 
mass was seen, by a ploughman, to descend toward 
the earth at a spot not far from where he was stand- 
ing. It threw up the soil on every side, and pene- 
trated some distance into the solid rock beneath. 
In 1807, a shower of stones, one weighing 200 lbs., 
fell at Weston, Connecticut. These aerohtes are 
sometimes seen to plunge downward into the earth, 
and are found while yet glowing. A mass thus fell in 



METEOES AND SHOOTING STARS. 197 

Soutli America, Avhicli was estimated to weigh fifteen 
tons. Wlien first discoyered, it was so hot as to 
prevent all approach. Upon its cooling, many efforts 
were made, by some travellers who were present, to 
detach specimens, but its hardness was too great for 
any tools which they possessed. There is a mass of 
meteoric iron in Yale College cabinet, weighing 
1,635 lbs. 

Aerolites consist of elements which are famihar. 
The analysis of these stellar masses gives us names 
as commonplace as if they had known a far 
less romantic origin — oxygen, sulphur, phosphorus, 
iron, tin, copper : in all, nineteen elements have 
been found. This fact is interesting as reveal- 
ing something of the chemistry of the region of 
space, concerning which we otherwise know nothing. 
The compounds, however, are very pecuhar, so as 
to distinguish an aerolite from any terrestrial sub- 
stance. For example, meteoric iron, a prominent 
constituent of aerolites, is an alloy that has never 
been found in terrestrial minerals. 

Meteors. — The records of meteors are still more 
wonderful. It is related that at Crema, Italy, one 
day in the 15th century, the sky at noonday be- 
came dark, — a cloud of appalHng blackness over- 
spreading the heavens. Upon this cloud appeared 
the semblance of a great peacock of fire flying over 
the town. This suddenly changed to a huge pyramid, 
that rapidly traversed the sky. Thence arose awful 
lightnings and thunderings, amid which there fell 



198 THE SOLAR SYSTEM. 

upon the plain great rocks, some of which weighed 
100 lbs. In 1803 a brilliant fireball (meteor) was 
seen traversing Normandy with great velocity, and 
some moments after, frightful explosions, like the 
noise of cannon or roll of musketry, were heard com- 
ing from a single black cloud hanging in a clear 
sky ; they were prolonged for five or six minutes. 
These discharges were followed by a great shower 
of stones, some weighing over 24 lbs. In 1819 a 
meteor was Avitnessed in Massachusetts and Mary- 
land, the diameter of which was estimated at half 
a mile. Its height was thought to be about 25 miles. 
In July, 1860, a brilliant fireball passed over the 
state of New York from west to east, and finally was 
seen to fall into the sea off Sandy Hook. 

Shooting Stars. — One of the earliest accounts of 
star-showers is that which relates how, in 472, the 
sky at Constantinople appeared to be alive with fly- 
ing stars and meteors. In some Eastern annals we 
are told that in October, 1202, " the stars appeared 
like waves upon the sky. They flew about hke 
grasshoppers, and were dispersed from left to right." 
It is recorded that in the time of King William 11. 
there occurred in England a wonderful shower of 
stars, which " seemed to fall like rain from heaven. 
An eye-witness seeing where an aerolite fell, cast 
water upon it, which was raised in steam with a 
great noise of boiling." Eastel says concerning it : 
*' By the report of the common people in this kynge'a 



METEORS AND SHOOTING STARS. 199 

time, diyerse great wonders were seene, and there- 
fore tlie kynge was told by diverse of his familiars, 
that God was not content with his lyvyng." 

In more modern times, the most remarkable ac- 
counts are those of the showers of November 12tli, 
1799, and 1833. Humboldt, in describing the former, 
says the sky was covered with innumerable fiery 
trails, which incessantly traversed the sky from 
north to south. From the beginning of the phenom- 
enon there was not a space in the heavens three 
times the diameter of the moon which was not filled 
every instant with the celestial fireworks, — large 
meteors blending constantly their dazzling brilliancy 
with the long phosphorescent paths of the shooting 
stars. The latter shower was most brilliant on this 
continent, and was visible from the lakes to the equa- 
tor. The scene was one of the most imposing grand- 
eur. Phosphoric lines swept over the sky like the 
flakes of a sharp snow-storm. Large meteors darted 
across the heavens, leaving luminous trains behind 
them that were visible sometimes for half an hour : 
they generally shed a soft white light ; occasionally, 
however, yellow, green, and other colors varied 
the scene. Irregular fireballs, almost stationary, 
glared in the sky; one especially, larger than the 
moon, hung in mid air over Niagara Falls and 
mingled its ghastly light with the foam and mist of 
the cataract. The shower commenced near mid- 
night, but was at its height about 5 a.m. In many 



200 THE SOLAR SYSTEM. 

sections of the country, tlie people were terror- 
stricken by the awful spectacle, and supposed that 
the end of the world had come. 

An inferior shower was seen in 1831 and 1832 ; 
and so also in the succeeding years, until 1839. 
These did not compare in brilliancy with the re- 
markable phenomenon of 1833. 

There was an interval of about 33 or 34 years 
between the great showers of 1799 and 1833 ; this 
seemed to indicate another shower in November, 
1866. The people of both hemispheres were Hter- 
ally awake to the subject. Newspapers aroused the 
most sluggish imagination with thrilling accounts of 
the scenes presented in 1799 and 1833. Extempore 
observatories were founded in every convenient point. 
Watchmen were stationed, and the city bells were to 
be rung on the appearance of the first wandering 
celestial visitor. The exact night was not definitely 
known, but for fear of a mistake, the 11th, 12th, and 
13th were generally observed. All painfully testify 
to those nights being clear and beautiful as moon- 
light and starlight could make them. The anxious 
vigils, the fruitless scannings of the sky, the disap- 
pointment, the meteors that were dimly thought to 
be seen — all these are recorded in the memory of 
the temporary astronomers of that year. While, 
however, the people of America were thus disap- 
pointed, there was being enacted in England a dis- 
play brilliant indeed, though inferior to the one of 



METEOKS AND SHOOTING STARS. 201 

1833. Tlie staff at Greenwich. Observatory counted 
about 8,000 meteors ; other observers, however, made 
a much lower estimate. Chambers, in describing the 
phenomena, says : " Of the large number of descrip- 
tions which came under my eye in manuscript and 
in print, the following is a fair example : 'From 11 J 
p. M. until 2 A. M. we were much interested in watch- 
ing the shooting stars ; anything so beautiful I never 
saw, especially about one o'clock, when they were 
most brilliant ;' and so on by the ream." On Novem- 
ber, 1867, the long-expected shower was seen in this 
country, but it failed to satisfy the public expecta- 
tion. The sky was, however, illumined with shoot- 
ing stars and meteors, some of which exceeded even 
Jupiter or Yenus in brilliancy. 

Numher of meteors and shooting stars. — In a paper 
lately read by Prof. Newton, it is estimated that the 
average number of meteors that traverse the atmos- 
phere daily, and which are large enough to be visi- 
ble to the eye on a dark clear night, is 7,500,000 ; 
and if to these the telescopic meteors be added, the 
number would be increased to 400,000,000. In the 
space traversed by the earth there are, on the aver- 
age, in each volume the size of our globe (including 
its atmosphere), as many as 13,000 small bodies, 
each one capable of furnishing a shooting star visi- 
ble under favorable circumstances to the naked eye. 

Annual periodicity of the star-shoivers. — On almost 
any clear night, from five to seven shooting stars 



202 THE SOLAR SYSTEM. 

may be seen per hour, but in certain months they 
are much more abundant. Arago names the fol-^ 
lowing principal dates : 

April 4-11 ; 17-25. October (about) 15. 
August 9-11. November 11-13. 

Oeigin. — ^AeroHtes, meteors, and falling stars all 
seem to have a common origin. They are produced 
by small bodies — planets in miniature — which are 
revolving, like our earth, about the sun. Their or- 
bits intersect the orbit of the earth, and if at any 
time they reach the point of crossing exactly with 
the earth, there is a collision. Their mass is so 
small, that the earth is not jarred any more than 
is a railway train by a pebble thrown against it. 

These small bodies may come near the earth and 
be drawn to its surface by the power of attraction ; 
or they may simply sweep through the higher re- 
gions of the atmosphere, and there escape its grasp ; 
or, finally, they may, under certain conditions, be 
compelled to revolve many times around the earth 
as satellites. Indeed, a French astronomer esti- 
mates that there is one now circling about the 
earth at a distance of 5,000 miles. This companion 
of our moon has a period of three hours and twenty 
minutes. The average velocity of these meteoric 
bodies or holides, as they are frequently called, is 
thirty-six miles per second — much greater than that 
of Mercury itself. As they sweep through the air. 



METEORS AND SHOOTING STAES. 203 

the friction partly arrests their motion, and converts 
it into heat and light. The body thus becomes visi- 
ble to ns. Its size and direction determine its ap- 
pearance. If very small, it is consumed in the upper 
regions, and leaves only the luminous trail of a shoot- 
ing star. If of large size, it may sweep along at a 
high elevation, or plunge directly toward the ground. 
Becoming highly heated in its course, it sheds a 
vivid light, while, unequally expanding, it explodes, 
throwing off large fragments which fall to the earth 
as aerolites, or continue their separate course as 
meteors. The cinders of the portion consumed rain 
down on us as fine meteoric dust. 

Meteoric Eings. — These little bodies, it is thought, 
do not generally revolve individually about the sun, 
but myriads of them are collected in several rings, 
and when the earth passes through one of these 
floating girdles, a star-shower follows. This would 
account for their regular appearance in certain sea- 
sons of the year. In the cut we see how one ring, 
intersecting the earth's orbit at two points, would 
account for the August and November showers. 
Another ring, more inclined to the earth's path, and 
crossing it nearer the aphelion point, would produce 
the April showers. 

Eecent investigators are inclined to the view that 
there are separate rings for each of the established 
periods, and that they are very elliptical. The No- 
vember ring seems to have its perihelion near the 



204 



THE SOLAR SYSTEM. 



ecliptic, and its aphelion beyond tlie orbit of Uranus ; 
while the August ring extends beyond the solar sys- 
tem. The day of the month in which the great No- 
vember shower occurs is becoming later at each re- 



Fi<r. 08. 




METEORIC RING. 



tiu-n ; hence it is believed that the nodes of that ring 
are slowly travelling eastward along the ecliptic. The 
meteoric bodies are supposed to be quite uniformly 
distributed through the August stream, but very un- 



METEOKS AND SHOOTING STARS. 205 

equally thiough the November one. On this ac- 
count, the former star-showers are quite regular, 
while the latter vary in brilliancy through periods 
of 33| years. 

Kelation between Meteoes and Comets. — The 
orbit of the November shower is found to be almost 
identical with that of the comet of 1866 ; while the 
August stream is in the track of the comet of 1862. 
It is a popular theory that these comets are only 
clusters of meteors crowded so closely together as to 
be visible by the reflected light of the sun. The single 
meteors are too small to be seen, except when they 
plunge into the earth's atmosphere and take fire. 
On the other hand, Herschel thinks that meteors are 
the dissipated parts of comets torn into shreds by 
the sun's attraction. 

Kadiant Point. — A star (m-) in the blade of the 
sickle is the point from which the stars in the Novem- 
ber shower seem to radiate, while one in Perseus (7) 
is the radiant point of the August shower. In the 
shower of 1866, two observers, who counted the 
falling stars at the rate of 2,500 per hour, saw only 
five which started from any other portion of the 
heavens than Leo. 

Meteorological effect. — The temperature, of 
August and November is said to be considerably in- 
creased by this ring of meteoric bodies, which pre- 
vents the heat of the earth from radiating into 
space. A corresponding decrease of temperature 
in February and May is caused by the sti-eam 



206 THE SOLAB SYSTEM. 

or ring of meteors coming between the sun and 
earth. 

Height. — Herschel estimates the average height 
of shooting stars above the earth at 73 miles at th6ir 
appearance and 52 at their disappearance. 

Weight. — Prof. Harkness estimates that the aver- 
age weight of shooting stars does not differ much 
from one grain. 

COMETS. 

"We come now to notice a class of bodies the 
most fascinating, perhaps, of any in astronomy. 
The suddenness with which comets flame out in 
the sky, the enormous dimensions of their fiery 
trains, the swiftness of their flight, the strange and 
mysterious forms they assume, their departure as 
unheralded as their advent — all seem to bid defiance 
to law, and partake only of the marvellous. Su- 
perstitious fears have always been excited by their 
appearance, and they have been looked upon in 
every age as 

" Threatening the world with famine, plague, and war ; 
To princes, death ; to kingdoms, many curses ; 
To all estates, inevitable losses ; 
To herdsmen, rot ; to ploughmen, hapless seasons ; 
To sailors, storms ; to cities, civil treasons." 

Thus the comet of 43 B. c, which appeared just 
after the assassination of Julius Caesar, was looked 
upon by the Romans as a celestial chariot sent to 
convey his soul heavenward. An old English writen 



COMETS. . 207 

observes : " Cometes signifie corruptions of the ayre. 
They are signs of earthquakes, of warres, of chang- 
yng kyngedomes, great dearthe of corn, yea, a com- 
mon death of man and beast." Another remarks : 
"Experience is an eminent evidence that a comet, 
like a sword, portendeth war ; and a hairy comet, or a 
comet with a beard, denoteth the death of kings, as 
if God and nature intended by comets to ring the 
knells of princes, esteeming bells in churches upon 
earth not sacred enough for such illustrious and emi- 
nent performances." 

Desckiption. — The term comet signifies a hairy 
body. A comet consists usually of three parts ; — the 
mtchus, a bright point in the centre of the head ; the 

Pig. 64. Pig. 65. 





COMET WITH OTTT A NUCLEUS. COMET WITH A NUCLEUS. 

coma (a hair), the cloud-like mass surrounding the nu- 
cleus ; and the tail, a luminous train extending gen- 
erally in a direction from the sun. There are comets 
without the tail, and others with several, while some 
are deprived of even the nucleus. These last consist 
merely of a fleecy mass, known to be comets from 



208 THE. SOLAR SYSTEM. 

their orbits and rapid motion. Comets are not con- 
fined, like the planets, to the limits of the zodiac, 
but appear in every quarter of the heavens, and move 
in every conceivable direction. When first seen, 
the comet resembles a faint spot of light upon tlie 
(lark background of the sky : as it approaches the 
sun the brightness increases, and the tail begins to 
show itself. Generally it is brightest near perihelion, 
and gradually fades away as it recedes, until it is 
finally lost, even to the telescope. 

The time of the greatest brilliancy depends 
somewhat on the position of the earth. If, as rep- 
resented in the figure, the earth is at a when the 
comet, moving toward perihelion, is at r, the comet 
will appear more distinct than Fig. 66 

when it is more distant at 5, al- 
though at the latter point it 
is really brighter. If, how- 
ever, the earth is at c or 5 at 
the time of perihelion, the com- 
et would be much more con- 
spicuous. Again, if the earth 

is passing from aioh during the time the comet is 
near the sun, it will appear less brilliant than if it 
were moving from c to d, as we should then be much 
nearer it during its greatest illumination. 

Number of Comets. — Kepler remarks that there 
are as many " comets in the heavens as fish in the 
sea." Arago has estimated that there are 17,500,000 
within the solar system, basing his calculations on the 




COMETS. 209^ 

number known to exist between the sun and Mercury. 
Of this vast number, few are visible to the naked 
eye, and a still less number attract observation, ow- 
ing to their inferior size and brilliancy. Many are 
doubtless lost to our sight by being above the hori- 
zon in the daytime. Seneca mentions that during a 
total solar eclipse, a large and splendid comet sud- 
denly made its appearance near the sun. 

Okbits of the Comets. — Comets form a part of 
the solar system, and are subject to the laws of grav- 
itation. Like the planets, they revolve around the 
sun, but they differ in the form of their orbits. 
While the planets move in paths varying but little 
from circular, and thus never depart so far from the 
sun as to be invisible to us, the comets travel in ex- 
tremely elongated (flattened) ellipses, so that they 
can be observed by us only through a very small 
portion of their paths. In Fig. 67 are represented the 
three general classes of their orbits. A comet travel- 
ling along an elliptical orbit, though it may pass far 
from the sun, will yet return within a fixed time ; 
one pursuing either a parabolic or hyperbolic curve 
cannot return, as the two sides separate from each 
other more and more. Many of the comets of the 
first class have been calculated, and they have re- 
peatedly visited our portion of the heavens ; whil-e 
those of the other classes, having once formed part 
of our system, go away forever, seeking perhaps in 
the far-off space another sun, which in turn they 
will abandon as thev have our own. 



210 



THE SOLAE SYSTEM. 



Fig.OT. 




THBEB FORMS OF COMETART OBBITB. 



Calculation of a Comet's Ketuen. — As we can 
observe so small a proportion of the entire orbit, it 
is very difficult, indeed oftentimes impossible, to 
decide whether it is an ellipse, hyperbola, or para- 
bola. A few are known to move in clearly ellip- 
tical paths, and their movements have been so 
accurately estimated that it is possible to predict 
their exact place in the starry vault on any given 



COMETS. 211 

day and hour. Tlie other comets may never return, 
or at least not for centuries hence. They may be 
paying our sun their first visit ; or if they have swept 
through the solar system before, it may have been 
at so remote a time that no record is preserved, 
even if it were not before the creation of man. Un- 
der these circumstances it is obviously extremely 
difficult to determine the times of these apparently 
erratic wanderers ; yet, in spite of all these obsta- 
cles, some have been tracked far into space beyond 
the telescopic view. For example, the comet of 
1844 is announced to pay a visit to the astronomers 
of the year of our Lord 101,844. The period of the 
comet of 1744, is fixed at 122,683 years. 

Distance from the Sun. — The comets at their 
periheHon sweep very near the sun. Thus the one 
of 1680 came where the temperature was estimated 
by Newton to be about 2,000 times that of red-hot 
iron. The nearest approach known is that of the 
comet of 1843, whose perihelion distance was but 
about 30,000 miles from the surface of the sun ; in 
fact, it doubled around that body in two hours' time. 
(Guillemin.) The greatest aphelion distance yet 
estimated is that of the comet of 1844, which is 
over 400,000,000,000 miles. The velocity varies, of 
course, with the position in the orbit. The comet of 
1680 moved in perihelion at the rate of over two 
hundred and seventy-seven miles per second ; while 
in aphelion its velocity is only about six miles per 
hour. 



212 THE SOLAR SYSTEM. 

Density of Comets. — The quantity of matter con- 
tained in a comet is exceedingly small. Telescopic 
stars even are visible through them. The comet of 
1770 became entangled among Jupiter's moons, and 
remained there four months without interfering with 
their movements in the least; indeed, so far from 
that, its own orbit was so much changed by the col- 
lision, that from a periodical return of 5J years, it 
has not been seen since. The same comet came 
within 1,400,000 miles of the earth without produ- 
cing any sensible effect. In 1861, w^e have good 
reason to suppose that the earth actually passed 
through the tail of a comet, its presence being 
indicated only by a peculiar phosphorescent mist. 
So that even should our earth run full-tilt against 
a comet, the shock would be quite imperceptible.* 
Still, however lightly we may speak of the proba- 
bility of such a collision, we must remember that 
there are comets of greater solidity. Donati's, for 
instance, is estimated to be about -^-^ the bulk of 
the earth. The concussion of such a body, moving 

* " However dangerous might be the shock of a comet, it might 
be so slight that it would only do damage at that part of the earth 
where it actually sti'uck ; perhaps even we might ciy quits, if, 
while one kingdom were devastated, the rest of the earth were 
to enjoy the rarities which a body coming from so far might 
bring to it. Perhaps we should be veiy surprised to find that the 
debns of these masses that we despised were formed of gold or 
diamonds; but who would be the more astonished — we or the 
comet-dwellers who would be cast on our eart.li ? What strange 
beings each would find the other !" Lettre sur la Gomete — (IVL 
De Maupertuis.) 



COMETS. • 213 

"witli the speed of a cannon-ball, would undoubtedly 
produce a very sensible effect. 

It is not understood whether comets shine by their 
own or by reflected light. If, however, their nuclei 
consist of white-hot matter, a passage through such 
a furnace would be any thing but desirable or satis- 
factory. After all the calculations of Astronomy, our 
only safety lies in that Almighty Power which traces 
the path and guides the course alike of planets and 
comets : He, whose eye marks the fall of the spar- 
row, sees as well the flight of the worlds He has 
created. 

Vaeiations in Foem and Dimensions. — Comets ap- 
pear to be subject to constant variations. They are 
now generally thought to decrease in brilliancy at 
each successive revolution about the sun. The same 
comet may present itself sometimes with a tail, and 
sometimes without. When the comet first appears, 
there is generally no tail visible, and the light is 
faint. As it approaches the sun, however, its bright- 
ness increases, the tail shoots out from the coma, 
and grows daily in length and splendor. Supernu- 
merary tails, shorter and less distinct than the prin- 
cipal one, dart out, but they generally soon disap- 
pear, as if from lack of material. The tail of the 
comet of 1843, just after the perihelion, increased in 
length 5,000,000 miles per day. As the tail thus 
extends, the nucleus is correspondingly contracted. 
Encke's comet, for instance, shrank in two months to 
T"r,ioi5- of its original volume. 



214 THE SOLAB SYSTEM. 

Hemakkable Comets. — Among the many comets 
celebrated in history, we shall only notice some of 
those that have appeared in the present century. 
The great comet of 1811 was a magnificent spec- 
tacle. The head was 112,000 miles in diameter ; the 
nucleus was 400 miles ; while the tail, of a beautiful 
fan-shape, stretched out 112,000,000 miles. The 
aphehon distance of this comet is fourteen times 
that of Neptune, or 40,000,000,000 miles. It is an- 
nounced to return in thii'ty centuries ! To what 
profound depths of space, beyond the solar system, 
beyond the reach of the telescope, must such a 
journey extend ! 

The comet of 1835 is commonly kno^vn as Halley's 
comet. This is remarkable as being the first comet 
whose period of revolution was satisfactorily estab- 
lished. Dr. Halley, on examining the accounts of 
the great comets of 1531, 1607, and 1682, suspected 
that they were only the reappearance of the same 
comet, whose period he fixed at about 75 years. He 
finally ventured to predict the return of the comet 
about the end of 1758 or beginning of 1759. Although 
Halley did not live to see his prophecy fulfilled, great . 
interest was felt in the result. It was not destined, 
however, for a professional astronomer to be the first 
to detect the comet. A peasant near Dresden saw 
it on Christmas night, 1758. The history of this 
comet, as it has been traced back by its period of 
seventy-five years, is quite eventful. It was seen in 
England in 1066, when it was looked upon with 



COMETS. 215 

dread as the forerunner of the victory of William of 
Normandy. It was then equal to the full moon in 
size. In 1456, its tail reached from the horizon to 
the zenith. It was supposed to indicate the success 
of Mahomet 11., who had already taken Constanti- 
nople, and threatened the whole Christian world. 
Pope Calixtus III., therefore, ordered extra Ave 
Marias to be repeated by everybody, and ako the 
church beUs to be rung daily at noon (whence origi- 
nated the custom now so universal). A prayer was 
added as follows : " Lord, save us from the devil, the 
Turk, and the comet." In 1223, it was considered 
the precursor of the death of Philip Augustus. The 
first recorded appearance of HaUey's comet was 
B. c. 130, when it was supposed to herald the birth of 
Mithridates. Its light then surpassed that of the sun. 

The comet of 1843 was so intensely brilliant that it 
was visible in fuU daylight. It was so near the 
sun as " almost to graze his surface." 

Eiicke^s comet has a period of only 3^ years. A 
most interesting discovery has been made from ob- 
servations upon its motion. The comet returns each 
time to its perihelion about 2 J hours earlier than the 
most perfect calculations indicate. Hence, Prof. 
Encke has been led to conjecture that space is filled 
with a thin, ethereal medium capable of diminishing 
the centrifugal force, and thus contracting the orbit 
of a comet. 

Donati's comet, which appeared in 1858, was the 
subject of universal wonder. Wlien first discovered, 



216 *THE SOLAR SYSTEM. 

in June, it was 240,000,000 miles from the earth. In 
August, traces of a tail were noticed, which expanded 
in October to about 50,000,000 miles in length. This 

Fig. 68. 




DONATI'8 COMBT. 



comet, though small, has never been exceeded in 
the brilliancy of the nucleus and the graceful cur- 
vature of the tail. It will return in about 2,000 
years. 



ZODIACAL LIGHT. 

Fiff. 69. 



217 




ZODIACAL LIGHT. 



ZODIACAL LIGHT. 

Description. — If we watch the western horizon in 
March or April, just after sunset, we shiill sometimes 
see the short twilight of that season illuminated by 

10 



218 THE SOLAK SYSTEM. 

a faint, tremulous liglit, of a conical shape, flashing 
upward, often as high as the Pleiades. In September 
and October, at early dawn, the same appearance 
can be detected near the eastern horizon. The 
light can be seen in this latitude only on the most 
favorable evenings, when the sky is clear and the 
moon absent. Even then, it will be frequently con- 
founded with the Milky Way or auroral lights. At 
the base it is of a reddish hue, where it is so bright 
as frequently to efface the smaller stars. In tropical 
regions the zodiacal light is perpetual, and shines 
with a brilliancy sufficient, says Humboldt, to cast a 
sensible glow on the opposite part of the heavens. 

Origin. — The commonly received opinion is, that 
it is caused by a faint cloud-like ring, perhaps a me- 
teoric zone, that surrounds the sun, and only be- 
comes visible to us when the sun himself is hidden 
below the horizon. Others maintain that, since it 
has been seen in tropical regions in the east and 
west simultaneously, it can be explained only on the 
theory of a "nebulous ring that surrounds the earth 
within the orbit of the moon." 



I^fo Sidereal JgjJt^m. 



" He telleth the number of the stars ; He calleth them all by 
their names." 

Psalm cxlvii. 4. 



THE SIDEREAL SYSTEM, 



THE STAES. 



In our celestial journey we have reached Neptune, 
the sentinel outpost of the solar system. We are 
now 2,750 milKons of miles from our sun. Yet we 
are apparently no nearer the fixed stars than when 
we first started. They twinkle as serenely there in 
the far-off sky as to us here on the earth. The 
heavens by night, with the exception of a few 
changes in the planets, look perfectly famihar. 
Between them and us there is a vast chasm which 
no imagination can bridge ; a distance so immense 
that figures are meaningless, and we can only call 
it space, — so profound that to us it is limitless, though 
beyond we see other worlds twinkling like distant 
lights over a waste of waters. 

We nevee see the staks. — This assertion seems 
almost paradoxical, yet it is strictly true. So far 
are the stars removed fi'om us, that we see only the 
light they send, but not the surface of the worlds 
themselves. They are merely glittering points of 



222 THE SIDEREAL SYSTEM. 

light. The most powerful telescope fails to produce 
a sensible disk. This constitutes a marked point 
of difference between a planet and a fixed star. 

The annual Paeallax of the fixed Staes. — When 
speaking of this subject on page 139, we said that 
183,000,000 miles, or the diameter of the earth's 
orbit, is taken as the unit for measuring the par- 
allax of the fixed stars. Yet when the stars are 
viewed from even these extreme points, they mani- 
fest so very slight a change of place, that to esti- 
mate it is one of the most delicate feats of astron- 
omy.* At the present time, it is considered that 
the star Alpha (a) Centauri in the southern heavens 
is the nearest to the earth. Its parallax is judged 
to be about 1". Its distance is more than 200,000 
times that of the earth from the sun, or nineteen tril- 
lions of miles. This is probably by no means its ex- 
treme distance, but merely the limit within which 
it cannot be, but beyond which it must be. These 
figures convey to our mind no idea of distance. Our 
imagination fails to grasp the thought, or to picture 
the vast void across which we are gazing. "We 
remember that light moves at the wonderful rate 
of 183,000 miles per second. A ray at this speed 
would plunge out into the abyss beyond Neptime, 
in one day, six times the distance of that planet 

* Prof. Aiiy says the star wMch gives the greatest parallax of 
any, presents an angle of 2". This is the angle at which a ckcle 
six-tenths of an inch in diameter would be seen at the distance of 
a mile I 



THE STAES. - 223 

from the sun. Yet it must sweep on at this pro- 
digious speed, day and night, for three years and 
nine months to span the gulf and reach a stopping 
point at the nearest fixed star. "To a spectator 
standing at a Centauri, the entire radius of the earth's 
orbit would be hidden by a thread ^V of ^^ i^^h in 
diameter, held at a distance of 650 feet from the 
eye." That is to say, a line 183,000,000 miles long, 
looked at broadside, would shrink into a mere point. 
If our sun were removed to that distance, it would 
shine with a Kght only equal to that of the north 
polar star, while its paraUax would be but ^ro of a 
second. 

This, we must remember, is the distance of the 
nearest fixed star. It has been estimated that the 
average time required for the light of the smallest 
stars which are visible to the naked eye to reach the 
earth is about 125 years. What, then, shaU we say 
of those far-distant ones, whose faint light appears 
as a mere fleecy whiteness even in the most power- 
ful telescopes ? The conclusion is irresistible, that 
the light we receive set out on its sidereal journey 
far back in the past, perhaps before the creation of 
man! 

Motion of the fixed Staes. — It will aid us still 
further in comprehending the immense distances of 
the stars, to learn that though they seem to be fixed, 
yet they are moving much more swiftly than any of 
the planets. Thus, Arcturus flies through space at 
the astonishing rate of about 200,000 miles per hour, 



224 THE SIDEKEAL SYSTEM. 

or nearly twice tliat of Mercury, and more than three 
times that of the earth. Yet, through all our life- 
time, we shall never be able to detect any change in 
its position. It requires three centuries for it to 
move over the starry vault a space equal to the 
moon's diameter. 

The staes aee suns. — The vast distance at which 
they are known to be, precludes the thought of their 
shining, like the planets or the moon, by reflecting 
back the Ught of our sun. They must be self-lumin- 
ous, and are doubtless each the centre of a system 
of planets and satellites. 

Our Sun a Star. — ^As we see only the suns of these 
distant systems, so their inhabitants see only the 
sun of ours, and that as a small star. 

Our system itself in motion. — Like all the other 
stars, our sun is in motion. It is sweeping onward, 
with its retinue of worlds, 150,000,000 miles per year, 
toward a point in the constellation Hercules. The 
Pleiades are thought to be the centre around which 
this great movement is taking place, but the orbit is 
so vast and the centre so remote, that nothing defi- 
nite is yet known. 

The Number of the fixed Stars. — As we look at 
the heavens on a clear night, the stars seem almost 
innumerable. To count them, one would think al- 
most as interminable a task as to number the leaves 
on the trees. It is, therefore, somewhat startling to 
leam that the enth^e number visible to the most 
piercing eyesight, does not exceed 6,000, while few 



THE STAKS. 



225 



can discern more than 4,000. This ilhision may be 
easily explained, when we remember how the impres- 
sion of a bright light remains upon the retina, as in 
the whirling of a firebrand. However, the number 



Fio;. 70. 




A PART OF THE CONSTELLATION OF THE TWINS. 

which may be seen with a telescope becomes alto- 
gether marvellous. In the cut is shown a portioD 



226 THE SIDEREAL SYSTEM. 

of the heayens where the naked eye sees but six 
stars. Could we examine the same region of the 
sky with more powerful instruments, new constella- 
tions would doubtless be descried in the infinite 
depths of space. 

Scintillation. — The twinkling of the fixed stars ig 
due to what is termed in Natural Philosophy " the 
interference of light." The air being unequally 
dense, warm, and moist in its various strata, trans- 
mits very irregularly the different colors of which 
white light is composed. Now one color prevails 
over the rest, and now another, so that the star ap- 
pears to change color incessantly. As the purity 
of the air varies, the twinkling of the stars also 
changes, although it is always greatest near the 
horizon. Humboldt says that at Cum ana, in South 
America, where the air is remarkably pure and uni- 
form in density, the stars cease to twinkle after they 
have risen 15° above the horizon. This gives to 
the celestial vault a peculiarly calm and soft appear- 
ance. 

Magnitude of the Stars. — As the telescope re- 
veals no disk of even the nearest stars, we know 
nothing of their comparative size. The finest spi- 
der's web, placed at the focus of the instrument, 
hides the star from the eye. When the moon passes 
in front of a star, the occultation is instantaneous, 
and not gradual, as in the case of the planets. Clas- 
sification depends, therefore, upon their relative 
brightness. The most conspicuous are termed stars 



THE STAKS. 227 

of the first magnitude. There are about twenty of 
these. The number of second magnitude stars in 
the entire heavens is about sixty-five ; of the third, 
about 200 ; of the fifth, 1,100 ; and of the sixth, 



Fig. 71. 



3,200. Few persons can see any smaller stars than 
those of the fifth or sixth magnitude. The ordinary 
telescope shows faint stars down to the tenth, while 
the more powerful instruments reveal those as low 
as the twentieth magnitude. 

The cause of the diffeeence in the brightness 
OF THE STAES. — This may result from a difference in 
their distance, size, or intrinsic brightness. "Whence 
it follows that the faintest stars may not be the most 
distant from the earth. 

Names of the Staes. — Many of the brightest stars 
received proper names at an early date ; as Sirius, 
Arcturus. The stars of each constellation are dis- 
tinguished by the letters of the Greek alphabet ; the 
brightest being usually called Alpha, the next Beta 
etc., — the name of the constellation, in the genitive 
case, being put after each. Ex., a Arietis, i^ Lyiae.-' 

* This means a of Aries, (5 of Lyra ; the genitive case in Latin 
being equivalent to the preposition of. 



228 the sideeeal system. 

The Greek Alphabet. 



A 


a 


Alpha 


N 


V 


I^u 


B 


^ 


Beta 


s 


1 


Xi 


r 


7 


Gamma 








Omicron 


A 


6 


Delta 


n 


"TT 


Pi 


E 


e 


Epsilon 


p 


P 


Rho 


Z 


? 


Zeta 


2 


r 


Sigma 


H 


7} 


Eta 


T 


T 


Tau 


e 


6 


Theta 


T 


U 


Upsilon 


I 


1 


Iota 


$ 


9 


Phi 


K 


X 


Kappa 


X 


X 


Chi 


A 


X 


Lambda 


i' 


4^ 


Psi 


M 


M- 


Mu 


Q 


w 


Omega 



When the Greek letters are exhausted, tlie Eoman 
alphabet is used in the same way. Star catalogues 
are issued, containing the stars arranged in the 
order of their Right Ascension, and numbered for 
convenience of reference. Argelander's Charts have 
300,000 stars marked in the northern hemisphere. 

The Constellations. — From the earliest ages, the 
stars have been arranged in constellations, for the 
purpose of more readily distinguishing them. Some 
of these groups were named from their supposed re- 
semblance to some figures, such as perching birds, 
pugnacious bulls, or contorted snakes, while others 
do honor to the memory of the classic heroes of an- 
tiquity. 

" Thus monstrous forms, o'er heaven's nocturnal arch. 
Seen by the saj^e, in pomp celestial march ; 



THE STAES. 229 

SJee Aries there his glittering bow unfold, 
And raging Taurus toss his horns of gold ; 
With bended bow the sullen Archer lowers, 
And there Aquarius comes with all his showers ; 
Lions and Centaurs, Gorgons, Hydras rise, 
And gods and heroes blaze along the skies." 

With a few exceptions, the likeness is purely fan- 
ciful. The heavens are much less of a menagerie 
than a celestial atlas would make them appear. 
The division into constellations is a mere relic of 
barbarism, entirely unworthy of modern civilization. 
Not only are the figures uncouth, and the origin 
often frivolous, but the boundaries are not distinct. 
Stars often occur under different names ; while one 
constellation encroaches upon another. As Cham- 
bers well remarks, " Aries should not have a horn in 
Pisces and a leg in Cetus, nor should 13 Argos pass 
through the Unicorn's flank into the Little Dog. 51 
Camelopardali might with propriety be extracted 
from the eye of Auriga, and the ribs of Aquarius re- 
leased from 46 Capricorni." While, however, the 
constellations are thus rude and imperfect, there 
seems little hope of any change. Age gives them a 
dignity that insures their perpetuation. 

Invention of the Constellations. — This goes 
back into ages of which no record remains. By 
some it has been ascribed to the Greeks. When the 
signs of the zodiac were named, they doubtless coin- 
cided with the constellations. Aries (the ram) was 
so called because it rose with the sun in the spring- 
time, and the Chaldean shepherds named it from 



230 THE SIDEKEAL SYSTEM. 

their flocks, their most valued possession. Then fol- 
lowed in order Taurus (the bull) and Gemini (the 
twins), called from the herds, which were esteemed 
next in value. At the summer solstice the sun ap- 
pears to stop, and, crab-like, to crawl backward; 
hence the name Cancer (a crab). When the sun is 
in Leo, the brooks being dry, the lion leaves his 
lurking-place and becomes a terror to all. Yirgo 
comes next, when the virgins glean in the summer 
harvest. At the autumnal equinox the days and 
nights are equally balanced, and this is beautifully 
represented by Libra (the scales). The vegetation 
decays in the fall, causing sickness and death ; the 
Scorpion, that stings as it recedes, is suggestive of 
this Parthian warfare. Sagittarius (the archer) tells 
of the hunting month. Capricornus (the goat), 
which delights in climbing lofty precipices, denotes 
how at the winter solstice the sun begins to climb 
the sky on his return north. Aquarius (the water- 
bearer) is a natural emblem of the rainy season. 
Pisces (the fishes) is the month for fishing. 

Signs and constellations do not agree. — By 
the precession of the equinoxes, as we have before 
described on page 121, the signs have fallen back 
along the echptic about 30°, so that those stars 
which were, in the infancy of astronomy, in the 
sign Aries (t) are now in Taurus (»), and those 
which were in the sign Pisces (^) are now in 
Aries (t). 



THE SIGNS. 



231 



The accompanying cut may illustrate this more 
clearly. 



Fig. 72. 




SIGNS AND CONSTEIiLATIONS, AS THET NOW COMPARE IN THE 
HEAVENS, THE FORMER HAVING FALLEN BACK, AND THE 
LATTER APPARENTLY ADVANCED, 30° EACH. 



Peemanence of the Constellations. — The figures 
which the stars form, and the general appearance of 
the constellations, are due to the position we occupy. 
Could we cross the gulf of space beyond Neptune, 
the stars now so f amihar to us would look strangely 
enough in their new groupings. As one in riding 
through a forest sees the trees apparently increase 
in size and open up to view before him, while they 



232 THE SIDEREAL SYSTEM. 

decrease in size and close in behind liim, forming 
clusters and groups whicli constantly change as he 
passes along ; so, as our earth travels with the solar 
system on its immense sidereal journey, the stars 
will grow larger and brighter in front, while those 
behind us will appear smaller and dimmer. Since, 
in addition to this, the stars themselves are in mo- 
tion with varying velocity and in different directions, 
the constellations must change still more rapidly, so 
as ultimately to transform entirely the appearance of 
the heavens. In time, the " bands of Orion" will 
be loosened, and the "Seven Sisters" will gHde 
apart into remote space. Such are the distances 
however, that, although these movements have been 
going on constantly, yet since the creation of man 
no variation has occurred that is perceptible, save to 
the Avatchful astronomer. Nothing in nature is as 
invariable as the stars. They are the standards of 
time. Myriads of years must elapse before new star- 
maps will be required. We need not, then, allow any 
fear of confusion to disturb us while we study the 
sky as it is. 

Value of the staes in practical life. — " The 
stars are the landmarks of the universe." They seem 
to be placed in the heavens by the Creator, not alone 
to elevate our thoughts and expand our conceptions 
of the infinite and eternal, but to afford us, amid the 
constant fluctuations of our own earth, something 
unchangeable and abiding. Every landmark about 
us is constantly changing, but over all shine the 



THE STARS. 233 

"eternal stars," each with its place so accurately 
marked, that to the astronomer and geographer no 
deception is possible. To the mariner, the heavens 
become a dial-plate, the figures on its face set with 
glittering stars, along which the moon travels as a 
shining hand that marks off the hours with an accu- 
racy no clock can ever rival. Standing on the deck 
of his vessel, far out at sea, a single observation of 
the sun or stars decides his location in the waste of 
waters as accurately as if he were at home, and had 
caught sight of some old landmark he had known 
from his boyhood. In all the intricacies of survey- 
ing, the stars furnish the only immutable guide. 
Our clocks vainly strive to keep time with the celes- 
tial host. Thus, by a wise provision of Providence, 
even in the most common affairs of life, are we com- 
pelled to look for guidance from the shifting objects 
of earth up to the heavens above. 

The views of the ancients. — Standing in the light 
of our present knowledge, the ideas of the ancients 
seem almost incredible, and we can hardly under- 
stand how they could have been seriously enter- 
tained. Anaximenes (550 B. c.) thought that the stars 
were for ornament, and were nailed like bright studs 
into the crystalline sphere. Anaxagoras (450 B. c.) 
considered that they were stones whirled up from the 
earth by the rapid motion of the ether around us, 
and that its inflammable properties set them on fire 
and caused them to shine as stars. Many schools 
of the Grecian philosophers — the Stoics, Epicu- 



234 THE SIDEEEAL SYSTEM. 

reans, etc. — believed that they were celestial fires kept 
alive by matter that constantly streamed up to them 
from the centre of the heavens. The stars were at 
one time said to feed on air ; at another, to be the 
breathing holes of the iiniverse. 

Theee zones of staes. — If we recall what was said 
on page 104, concerning the paths of the stars and 
appearance of the heavens at different seasons of 
the year, we shall see that the constellations are nat- 
urally divided into three zones. The first embraces 
those which are visible through the entire year ; the 
secoiid, those whose orbits can be seen only in part 
on any given night ; and the third , those whose paths 
just graze our southern horizon, or never pass 
above it. 

THE CONSTELLATIONS. 

Nobtheen Ciecumpolae Constellations. — These 
constellations in our latitude are visible every 
night. They may be easily traced by holding the 
book up toward the northern sky in such a way 
that Polaris and the Dipper on the map and in the 
heavens agree in position, and then locating the 
other constellations by comparison. As they revolve 
about Polaris, their places will vary with every 
successive night through the year. The cut repre- 
sents them as they are seen at midnight of the win- 
ter solstice. At 6 p. M. of that day the right-hand 
side of the map should be held downward, and the 



THE CIKCUMPOLAR CONSTELLATIONS. 235 

Big Dipper will be directly below tlie nortli star. 
At 6 A. M. the left-hand side should be at the bot- 
tom, and the Dipper will be above Polaris. From 
day to day this aspect will change, each star coming 

(Map No. 1.)— Fig. 73. 




NOPvTHEKN CIRCUMPOLAK CONSTELLATION 



a little earlier to the meridian, or to its position on 
the preceding night. The rate of this progression 
is six hours, or 90°, in three months. 

TIrsa Major is represented under the figure of a 
great hear. It contains 138 stars visible to the 
naked eye. The constellation has been celebrated 



236 THE SBDEEEAL SYSTEM. 

among all nations. It is remarkable that the shep- 
herds of Chaldea in Asia, and the Iroquois Indians 
of America, gave to it the same name. 

Frincipal stars. — A noticeable cluster of seven 
stars — six of the second and one of the fourth mag- 
nitude — forms what is famiHarlj termed " The Dip- 
per.''' In England it is styled Charles's Wain, from 
a fancied resemblance to a wagon drawn by three 
horses tandem. Mizar (^) has a minute companion, 
Alcor, which Humboldt teUs us could be rarely 
seen in Europe. A person with good eyesight may 
now readily detect it. Megrez {6), at the junction of 
the handle and the bowl, is to be marked particu- 
larly, since it lies almost exactly in the colure passing 
through the autumnal equinox. Dubhe and Merak 
are termed " The Fointers,'' since they always point 
out the polar star. The bear's right fore paw and 
hinder paw are each marked by two smaU stars, as 
shown in the cut ; a similar pair nearly in line with 
these denote the left hinder paw (see I, Fig. 76). 
Each paw is 15° apart. 

Mythological history. — Diana had a very beau- 
tiful attendant named Callisto. Juno, the queen of 
heaven, becoming jealous of the maid, transformed 
her into a bear. 



The prostrate wretch lifts up her head, in prayer, 
Her arms grow shaggy, and deformed with hair ; 
Her nails are sharpened into pointed claws, 
Her hands bear half her weight and turn to paws. 
Her lips, that once would tempt a god, begin 
To grow distorted in an ugly grin. 



THE CIRCUMPOLAE CONSTELLATIONS. 237 

♦ 

And lest the supplicating brute miglit reach 
The ears of Jove, she was deprived of speech. 
How did she fear to lodge in woods alone, 
And haunt the fields and meadows once her own i 
How often would the deep-mouthed dogs pursue, 
Whilst from her hounds the frighted hunters flew. 

Some time afterward, Callisto's son, Areas, being 
out hunting, pursued his mother and was about to 
transfix her with his upHfted spear, when Jupiter in 
pity transferred them both to the heavens, and 
placed them among the constellations as Ursa Ma- 
jor and Ursa Minor. 

Ursa Minor is represented under the figure of a 
small bear. It contains twenty-four stars, of which 
only three are of the third, and four of the fourth 
magnitude. 

Principal stars. — A cluster of seven stars forms 
what is termed the " Little Dipper.^'' Three of them 
are small, and are seen with difficulty. Polaris, at 
the extremity of the handle, has been known from 
time immemorial as the North Polar Star. Among 
the Greeks it was styled Cynosure. Until the ma- 
riner's compass came into use, it was the star 

" Whose faithful beams conduct the wandering ship 
Through the wide desert of the pathless deep." 

Polaris does not mark the exact position of the 
pole, since that is about 1J° toward the Pointers. 
This distance will gradually diminish, until in time 
it will be only J° : then it will increase again, imtil 
in the lapse of ages — 12,000 years hence — the bril- 



238 THE SIDEREAL SYSTEM. 

liant star a Lyrse will fulfil the office of polar star 
for those who shall then live on the earth. 

Curious fact concerning the Pyramids. — Of the 
nine Pyramids which are standing at Gizeh, Egypt, 
six have openings facing the north. These lead to 
straight passages which descend at a uniform angle 
of about 26° and are parallel with the meridian. If 
we suppose a person, dOOO years ago, standing at 
the lower end of one of these passages, and looking 
out, his eye would strike the sky near the star 
Thuban, which was then the polar star. The 
supposed date of the building of these Pyramids 
(2123 B. c.) agrees with that epoch, and very naturally 
suggests that the builders had some special design 
in this pecuHar construction. 

The distance of Polaris is so great, that though the 
star is moving through space at the rate of ninety 
miles per minute, this tremendous speed is imper- 
ceptible to us. It requires nearly fifty years for its 
light to reach the earth ; so that when we look at Po- 
laris, we know that the ray which strikes our eye 
set out on its journey through space haK a cen- 
tury ago. We cannot state positively that the star 
is now in existence, since if it were destroyed to-day 
it would be fifty years before we should miss it. 

Calculation of latitude from Polaris. — By an ob- 
server at the equator, Polaris is seen at the 
horizon. If he advances north, the horizon is de- 
pressed and Polaris seems to rise in the heavens. 
When it has reached the height of a degree, the ob- 



THE CIRCUMPOLAE CONSTELLATIONS. 239 

server is said to have passed over a degree of lati- 
tude on the earth's surface. As he moves further 
north, the polar star continues to ascend ; its dis- 
tance above the horizon denoting the latitude of 
each place in succession, until at the north pole, if 
one could reach that point, Polaris would be seen 
directly overhead. 

Draco is represented under the figure of a long 
sinuous serpent, stretching between Ursa Major and 
Ursa Minor, nearly encircling the latter constellation, 
and finally reaching out its head almost to the body 
of Hercules. 

Principal stars. — Four small stars form a quad- 
rilateral figure at the head; .a fifth of the fourth 
magnitude (Rastaban), scarcely visible, marks the 
end of the nose ; several scattered groups and deli- 
cate triangles of small stars, denote the position of 
the various coils of the body ; thence, an irregular 
line of stars traces the dragon's tail around between 
Ursa Major and Ursa Minor. Thuban lying midway 
between 7 of the Little Dipper and ^ of the Big Dip- 
per, is noted as the polar star of forty centuries ago. 

BIythological history. — Many accounts are given of 
the origin of this constellation, as indeed there are of 
almost everj^ one in the heavens. The prevalent 
opinion is, that it is the dragon which Cadmus slew. 
The story is as follows. Jupiter had carried off Eu- 
ropa. Agenor, her father, sent her brother Cadmus 
in pursuit of his lost sister, bidding him not to re- 
turn until he was successful in his search. After a 



240 THE SIDEREAL SYSTEM. 

time, Cadmus, weary of his wanderings, inquired of 
tlie oracle of Apollo concerning the fate of Eui'opa. 
He was told to cease looking for his sister, to fol- 
low a cow as a guide, and when she rested, there 
to build a city. Hardly had Cadmus stepped out 
of the temple, when he saw a cow slowly walking 
along. He followed her until she came upon the 
broad plains where Thebes afterward stood. Here 
she stopped. Cadmus wishing to offer a sacrifice to 
Jupiter in gratitude for the delightful location, sent 
his servants to seek for water. In a dense gi;ove 
near by was a fountain guarded by a fierce dragon 
(Deaco), and sacred to Mars. The Tyrians approach- 
ing this and attempting to dip up some water, were 
attacked, and many of them killed by that enormous 
serpent, whose head overtopped the tallest trees. 
Cadmus, becoming impatient, went in search of his 
men, and on coming to the spring, saw the sad disas- 
ter. He forthwith fell upon the monster, and after a 
severe battle succeeded in slaying him. While stand- 
ing over his conquered foe, he heard a voice from 
the ground bidding him take the dragon's teeth and 
sow them. He obeyed. Scarcely had he finished 
ere the earth began to move and the points of spears 
to prick through the surface. Next nodding plumes 
shook off the clods, and the heads of armed men pro- 
truded. Soon a great harvest of warriors covered 
the entire plain. Cadmus, in terror at the appear- 
ance of these giants, whom he termed Sparti (the 
Soivn), prepared to attack them, when suddenly they 



THE CIECUMPOLAB CONSTELTATIONS. 241 

tnirned upon themselves, and never ceased their war- 
fare until only five of the crowd sur\ived. These 
making peace with each other, joined Cadmus and 
assisted him in building the city of Thebes. 

Cepheus is represented as a king in regal state, 
with a crown of stars on his head, while he holds in 
his hand a sceptre which is extended toward his 
wife, Cassiopeia. The constellation contains thirty- 
five stars visible to the naked eye. 

Principal stars. — The brightest star is Alderamin 
(a), in the right shoulder. Alphirk (/3), in the girdle, 
is at the common vertex of several triangles, which 
point out respectively the left shoulder (i), the left 
knee (7), and the right foot. The head, which lies 
in the Milky Way, is marked by a delicate little 
triangle of three stars. This forms, with a, ^, and 2, 
quite a regular quadrilateral figure. A bright little 
star of the fifth magnitude, close to Polaris, points 
out the left foot. 

Cassiopeia^ is represented as a queen seated on 
her throne. On her right is the king, on her left 
Perseus, her son-in-law, and above her is Androme- 
da, her daughter. The constellation contains fifty- 
five stars visible to the naked eye. 

Principal stars. — A line drawn from Megrez (5), in 
Ursa Major, through Polaris and continued an equal 
distance beyond, will strike Caph (^) in Cassiopeia. 
This star is noticeable as marking, with the others 

* For mythological history, see Perseus and Andromeda. 

11 



242 THE SIDEREAL SYSTEM. 

named, the equinoctial colure, and as being on the 
same side of the true pole as Polaris. The principrd 
stars form the figure of an inverted chair, which ** 
very striking and may be easily traced. 

EQUATOEIAL CONSTELLATIONS. 

The constellations we shall now describe lie south 
of the circumpolar groups. Only a portion of their 
paths is above our horizon. In using the maps, the 
observer is supposed to stand with his back toward 
Polaris, and to be looking directly south. Com- 
mencing with the constellation Perseus, so intimately 
connected with the other members of the royal fam- 
ily just described, we pass eastward in our survey 
and notice the various constellations as they slowly 
defile in silent march across the sky. The first map 
represents the constellations on or near the meridian 
at nine o'clock in the evening of the winter solstice. 
On the evening of the autumnal equinox, the left- 
hand side of the map should be turned downward 
toward the eastern horizon. On the evening of the 
vernal equinox, the right-hand side should be turned 
to the western horizon. At these different times, the 
stars, though preserving then- relative positions, wiU 
be diversely inclined to the horizon. As the stars 
apparently move westward at the rate of 15° per 
hour, the time of the evening determines what stars 
^vi^ be visible, and also their distances above the 
horizor 



EQUATORIAL CONSTELLATIONS. 243 

(Map No. 2)— Fig. 74. 




Perseus is represented as brandishing an enor- 
mous sword in his right hand, while in his left he 
holds the head of Medusa. The constellation com- 
prises eighty-one stars visible to the naked eye. 

Principal stars. — The most prominent figure is 
called the segment of Perseus. It consists of several 
stars arranged in a line curving toward Ursa Major. 
Algenib (a), the brightest of these, is of the second 
magnitude. Algol, in the midst of a group of small 
stars, marks the head of Medusa. Between the 
bright stars of Perseus and Cassiopeia is a beautiful 
star-cluster visible to the naked eye. 

BIythological history. — Perseus, fi'om whom this 
constellation was named, was the son of Jupiter and 
Danae. His grandfather, Acrisius, having been in- 
formed by the oracle that his grandson would be the 



244 THE SIDEREAL SYSTEM. 

instniment of his death, put the mother and child in 
a coffer and set them adrift on the sea. Fortunately, 
they floated near the island Seriphus, where they 
were rescued and kindly treated by a brother of Pol- 
ydectes, king of the country. When Perseus had 
grown up, he was ordered by Polydectes to bring 
him, as a marriage gift, the head of Medusa. Now 
Medusa was once a beautiful maiden, who dared to 
compare her ringlets with those of Minerva ; where- 
upon the goddess changed her locks into hissing 
serpents, and made her features so hideous, that she 
turned to stone every living object upon which she 
fixed her Gorgon gaze. Perseus was at first quite 
overpowered at the thought of undertaking this en- 
terprise, but was visited by Mercury, who promised 
to be his guide, and to furnish him with his winged 
shoes. Minerva loaned him her wonderful shield, 
that was bright as a mirror. The Nymphs gave him, 
in addition, Pluto's helmet, which made the bearer 
in^dsible. Thus equipped, Perseus mounted into the 
air and flew to the ocean, where he found the three 
Gorgons, of whom Medusa was one, asleep. Fear- 
ing to gaze in her face, he looked upon the image 
reflected in Minerva's shield, and with his sword 
severed Medusa's head from her body. The blood 
gushed forth, and with it the winged steed Pegasus. 
Grasping the head, Perseus flew away. The other 
Gorgons awaking, pursued him, but he escaped their 
search by means of Pluto's helmet. Flying over the 
wilds of Libya, in his aerial route, drops dripping 



EQUATOKIAL CONSTELLATIONS. 245 

from the gory head of the monster produced the in- 
numerable serpents for which that country was after- 
ward celebrated. 

Andromeda is represented as a beautiful 
maiden chained to a rock. 

Frindpal stars. — Algenib and Algol in Perseus 
form, with Almaach (7) in the left foot of Androme- 
da, a right-angled triangle opening toward Cassio- 
peia. This figure is so perfect, that the stars may 
be easily recognized. The girdle is pointed out by 
Merach (^), and two other stars which form a line 
slightly curving toward the right foot. The breast is 
denoted by a very delicate triangle composed of 
three stars, d of the fourth magnitude, another of the 
fifth magnitude just south, and an exceedingly minute 
star a little at the west. Alpheratz (a), in the head 
of Andromeda, belongs also to Pegasus. This star, 
with three others, all of the second magnitude, con- 
stitute the " Great Square of Pegasus'' Their names 
are Algenib (X), Markab (a), and Scheat {(i). The 
brightest stars of these two constellations form a 
figure strikingly like the Big Dipper. Algenib and 
Alpheratz lie in the equinoctial colure which passes 
through Caph. 

Mythological history. — Cassiopeia had boasted that 
her daughter Andromeda was fairer than the Sea- 
nymphs. They appealed, in great indignation, to 
Neptune, who sent a sea-monster (Cetus) to devas- 
tate the coast of Ethiopia. To appease the deities, 
her father Cepheus was directed by the oracle to 



246 THE SIDEEEAL SYSTEM. 

bind his daughter to a rock, to be devoured by Cetus. 
Perseus returning from the destruction of Medusa, 
saw Andromeda in her forlorn condition. Struck by 
her beauty and tears, he offered to liberate her 
at the price of her hand. Her parents consented 
joyfully, and, in addition, offered a royal dower. 
Perseus slew the terrible monster, and freeing An- 
dromeda, restored her to her parents. All the promi- 
nent actors in this scene were honored with seats 
among the constellations. The Sea-nymphs, it is 
said, in petty spite of Cassiopeia, prevailed that she 
should be placed where for half of the time she 
hangs with her head downward — a fit lesson of hu- 
mility. Cepheus, her husband, shares in her pun- 
ishment. 

Aries, the ram, was anciently the first constella- 
tion of the zodiac. It is now the first sign, but the 
second constellation. On account of the precession of 
the equinoxes, the constellation Pisces occupies the 
first sign. 

Principal stars. — The most noted star is a Arietis 
(Alpha of Aries, more commonly called simply Arie- 
tis), in the right horn. This lies near the path of the 
moon and is one of the stars from which longitude is 
reckoned. A line drawn from Almaach to Arietis 
will pass through a beautiful figure of three stars 
called the The Teiangles. 

Mythological history. — Phryxus and Helle were the 
oJiildren of Athamas, king of Thessaly. Being per- 
secuted by Ino, their step-mother, they were com- 



EQUATOBIAL CONSTELLATIONS. 247 

pelled to flee for safety. Mercury provided them a 
ram which bore a golden fleece. The children were 
no sooner placed on his back than he vaulted into 
the heavens. In their aerial journey Helle becom- 
ing dizzy fell off into the sea, which was afterward 
called the Hellespont, now the Dardanelles. Phryx- 
us coming in safety to Colchis, on the eastern shore 
of the Black Sea, offered the ram in sacrifice to Ju- 
piter, and gave the golden fleece to Aetes, his pro- 
tector. The Argonautic expedition in pursuit of this 
golden fleece, by Jason and his followers, is one of 
the most romantic of mythological stories. It is, 
undoubtedly, a fanciful account of the first impor- 
tant maritime expedition. Rich spoils were the 
prizes to be secured. 

Taurus consists only of the head and shoulders 
of a huU^ which is represented in the act of plunging 
at Orion. 

Principal stars. — The Hyades, a beautiful cluster 
in the head, forms a distinct V. The brightest of 
these is Aldebaran, a fiery red star of the first mag- 
nitude. The Pleiades,^' or the " Seven Sisters," as 
it is sometimes termed, is the most conspicuous 
group in the heavens. It contains a large number of 
stars, six of which are visible to the naked eye. 
There were said to have been anciently seven, but 
Erlectra left her place that she might not behold the 
ruin of Troy, which was founded by her son Dar- 

* Job, xxxviii. 31 ; Amos, v. 8. 



i^48 THE SIDEREAL SYSTEM. 

danus. Others say that the " lost Pleiad'' was Mero- 
pe, who married a mortal. Alcyone is the most dis- 
tinctly seen. El Nath (/3) and ^ point out the horns 
of Taurus. 

Mythological history, — This is the animal whose 
form Jupiter assumed when he bore off Europa. The 
Pleiades were the daughters of Atlas, and Nymphs 
of Diana's train. They were distinguished for their 
unblemished virtue and mutual affection. The hunt- 
er Orion having pursued them one day, they prayed 
to the gods in their distress. Jupiter in pity trans- 
ferred them to the heavens. 

Auriga, the Charioteer or Wagoner, is represented 
as a man resting one foot on a horn of Taurus, and 
holding a goat and kids in his left hand and a bridle 
in his right. 

The principal stars are arranged in an irregular 
five-sided figui*e, which is very noticeable. Capella, 
the goat-star, is of the first magnitude. It travels 
in its orbit 1,800 miles per minute; and it takes 
seventy-two years, or a man's lifetime, for its light 
to reach the earth. Near by is a delicate triangle 
formed of three small stars, called the Kids. Men- 
kalini (^) is in the right shoulder, ^ in the right 
hand, /3 (common to Auriga and Taurus) the right 
foot and i the left foot. Capella, /3, and 5 (a star in 
the head) form a triangle. The origin of this con- 
stellation is unknown. 

Fisces, the fishes, is represented by two fishes 
tied together by a long ribbon. It consists of small 



EQUATORIAL CONSTELLATIONS. 



249 



stars, which can -be traced only upon a clear night, 
and in the absence of the moon. 

Cetus, the whale, is a huge sea-monster, slowly 
ploughing his way westward, near the horizon. 11 
may be easily found, under favorable circumstances, 
by means of the numerous figures given in the map. 

(Map No. 3)— Fi^. 75. 




Gemini, the Twins, represents the twin brothers 
Castor and Pollux. 

The principal stars are Castor and Pollux, which 
are of the first and second magnitudes. The latter 
is also one of the stars from which longitude is reck- 
oned by means of the Nautical Almanac. The con- 
stellation is clearly distinguished by means of two 
nearly parallel rows of stars, which by a slight eflbrt 



250 THE SIDEREAL SYSTEM. 

of the imagination may be extended into the constel- 
lations Taurus and Orion. 

Mythological history. — Castor and Pollux were no- 
ted — the former for his skill in training horses, the 
latter for boxing. They were tenderly attached to 
each other, and were inseparable in all their adven- 
tures. They accompanied Jason on the Argonautic 
expedition. A storm having arisen on this voyage, 
Orpheus played on his wonderful lyre and prayed to 
the gods ; whereupon the tempest was stilled, and 
star-like flames shone upon the heads of the twin- 
brothers. Sailors, therefore, considered them as pa- 
tron deities,* and the balls of electric flame seen on 
masts and shrouds, now called St. Elmo's fire, were 
named after them. Afterward, Castor was slain. 
Pollux being inconsolable, Jupiter offered to take 
him up to Olympus, or to let him share his immor- 
tality with his brother. Pollux preferred the latter, 
and so the brothers pass * alternately one day under 
the earth, and the next in the Elysian Fields. Not 
only did sailors thus think them to watch over navi- 
gation, but they were believed to return, mounted on 
snow-white steeds and clad in rare armor, to take 
part in the hard-fought battle-fields of the Eomans. 



' Back comes the chief in triumph, 
Who in the hour of fight 
Hath seen the great Twin Brettiren, 
In harness on his right. 



*Acts, xxviii. 11. 



EQUATOEIAL CONSTELLATIONS. 251 

Safe comes the ship to haven, 
Through billows and through gales, 

If once the great Twin Brethren 
Sit shining on the sails."— Xays of Ancient Rome. 

Orion is represented under tlie figure of a hunter 
assaulting Taurus. He has a sword in his belt, a 
club in his right hand, and the skin of a Hon in his 
left. This is one of the most clearly defined and 
conspicuous constellations in the heavens. 

Principal stars. — Four brilliant stars, in the form of 
a parallelogram, mark the outlines of Orion. Betel- 
geuse, a beautiful ruddy star of the first magnitude, 
is in the right shoulder ; Bellatrix (7), of the second 
magnitude, is in the left shoulder ; Eigel, of the first 
magnitude, is in the left foot ; and Saiph (x), of the 
third magnitude, is in the right knee. Two small 
stars near >■ form with it a small triangle, which is 
itself the vertex of a larger triangle composed of \ 
7, and Betelgeuse. Near the centre of the parallel- 
ogram are three stars forming " the Belt of Oricm,^^ 
called also the " Bands of Orion" (Job, xxxviii. 31), 
Jacob's rod, but more commonly the " EU and Yard." 
They received the last name because they form a 
line just 3° long, divided in equal parts by a star 
in the centre. These divisions are useful for meas- 
uring the distances of the stars. Kunning from the 
belt southward, is an irregular line of stars which 
marks the sword ; and west of Bellatrix is a curved 
line denoting the Hon's sMn. South of Orion are four 
stars forming a beautiful figure styled the Hare. 



262 THE SIDEREAL SYSTEM. 

Mythological History. — Orion was a famous hunter. 
Becoming enamored of Merope^ he desired to mar- 
ry her. (Enopion, her father, opposing the choice, 
took a favorable opportunity and put out the eyes of 
the unwelcome suitor. The bhnded hero followed 
the sound of a Cyclop' s hammer until he came to Yul- 
can's forge. He, taking pity, instructed Kedalion to 
conduct him to the abode of the sun. Placing his 
guide on his shoulder, Orion proceeded to the east. 
and at a favorable place 

" Climbing up a narrow gorge, 
Fixed his blank eyes upon the sun." 

The healing beams restored him to sight. As a pim- 
ishment for having profanely boasted that he was 
able to conquer any animal the earth could produce, 
he was bitten in the heel by a scorpion. Afterward, 
Diana placed him among the stars ; where Sieius 
and Peocyon, his dogs, follow him, the Pleiades fly 
before him, and far remote is the Scorpion, by whose 
bite he perished. 

Canis Major and Cants Minor contain each a 
single star of the first magnitude, Sirius and Procyon. 
These two, Avith Betelgeuse, Phaet in the Dove, and 
Naos in the Ship, form a huge figure known as 
the Egyptian X. Sirius, the dog-star, is the most 
brilliant star in the heavens. It travels at the rate 
of 840 miles per minute. Twenty-two years are 
required for its light to reach the earth ; its distance 
being estimated at 1,375,000 times that of the sun 
from us. If its intrinsic brilliancy be the same as 



EQUATOKIAL CONSTELLATIONS. 253 

that of our sun, its diameter at that distance must be 
fifteen times as great, or 12,000,000 miles. Prob- 
ably these estimates fall far below the reahty of this 
magnificent orb. 

(Map No. 4)— Fig. 76. 




Leo is represented as a rampant lion. It is one of 
the most beautiful constellations in the zodiac. 

The 'principal stars are arranged in the form of a 
sickle. Eegulus, in the handle, is a brilliant star of 
the first magnitude. It is one of the stars from which 
longitude is reckoned. It is almost exactly in the 
ecliptic. Zosma (8) lies in the back of the hon, & in 



254 THE SIDEBEAL SYSTEM. 

the thigh, and Denebola, a star of the second mag- 
nitude, in the brush of the tail. 

Cancer includes the stars which lie irregularly 
scattered between Gemini, Head of Hydra, Procyon, 
and Leo. In the midst of these is a cluster of stars, 
visible to the naked eye, called Presepe or the Bee- 
hive. 

Virgo is represented as a beautiful maiden with 
folded wings, bearing in her left hand an ear of 
corn. 

The principal star is Spica Virginis, in the ear of 
corn. It is of the first magnitude, and is used for 
determining longitude at sea. Denebola, Cor Caroli, 
(a), -Arcturus (Map No. 5), and Spica form a figure 
about 50° in length from north to south, called the 
Diamond of Yirgo. The other stars may be easily 
traced by means of the map. 

Mythological History. — Yirgo was the goddess As- 
trsea. According to the poets, the early history of 
man was the golden age. It was a time of inno- 
cence and truth. The gods dwelt among men, and 
perpetual Spring delighted the earth. Next came 
the silver age, less tranquil and serene, but still the 
gods lingered and happiness prevailed. Then fol- 
lowed the brazen and iron ages, when wickedness 
reigned supreme. The earth was wet with slaughter. 
The gods left the abodes of men one by one, As- 
troea alone remaining ; until finally she too, last of all 
the immortals, bade the earth farewell. Jupiter 
thereupon placed her among the constellations. 



EQUATORIAL CONSTELLATIONS. 255 

Sydva is a long straggling serpent having its head 
near Procjon and extending its tail beyond Yirgo, 
a total distance of more than 100°. 

The principal star is Cor Hydrse, of the second 
magnitude. It is a lone star, and may be easily fonnd 
by a line drawn from y Leonis through Eegulus, 
and continued about 23°. The head is marked by a 
rhomboidal figure of four stars of the fourth magni- 
tude lying near Procyon. Several delicate triangles 
may be formed of them and other small stars lying- 
near. The Crater or Cup is a beautiful and very 
striking semicircle of six stars of the fourth magni- 
tude du-ectly south of ^ Leonis. Corvus, the raven, 
b'es 15° east of the Cup. e Corvi is in the equinoctial 
colure. 

Mythological history. — Hydra was a fearful serpent 
which in ancient times infested the lake Lerna. Its 
destruction constituted one of the twelve labors of 
Hercules. The Crow was formerly white, it is said, 
but was changed to its raven tint on account of its 
proneness to tale-bearing. 

Cor Caroli («.) is marked by a line passing from 
Benetnasch {y]) through Berenice's Hair to Denebola 

JBerenice^s Hair is a beautiful cluster midway 
between Cor Caroli and Denebola. Nearby is a single 
bright star of the fourth magnitude. 

Mythological history. — Berenice was the wife of 
Ptolemy. Her husband going upon a dangerous ex-« 
pedition, she promised to consecrate her beautiful 



256 



THE SIDEREAL SYSTEM. 



tresses to Venus if lie should return in safety. Soon 
after the fulfilment of this vow the hair disappeared 
from the temple where it had been deposited. 
Berenice being much disquieted at this loss, Conon, 
the astronomer, announced that the locks had been 
transferred to the heavens. In proof of which, he 
pointed out this cluster of hitherto unnamed stars. 
All parties were satisfied with this happy termina- 
tion of the difficulty. 

(Map No. 5)— Fig. 77. 




Bootes, the bear-driver, is represented as a hunts- 
man grasping a club in his right hand, while in his 
left he holds by the leash his two greyhounds, with 
which he is pursuing the Great Bear continually 
around the north pole. 

Principal stars. — Arcturus,* a magnificent red star 
•■• Job, ix. 9. 



EQUATORIAL CONSTELLATIONS. 257 

of the first magnitude, is in the left knee. It forms 
a triangle with Denebola and Spica, and also one 
with Denebola and Cor CaroH. It travels in its orbit 
fifty-four miles per second, or more than three times 
as fast as the earth. Its light reaches the earth in 
about twenty-six years. Mirac (s) lies in the girdle, 
S in the right shoulder, Alkaturops (f/-) in the club, (3 
in the head, and Seginus (7) in the left shoulder. 
Seginus forms with Cor Caroli and Arcturus a tri- 
angle, right-angled at Seginus. Three small stars 
in the left hand of Bootes He near Benetnasch. 

Mythological history. — Bootes is supposed to have 
been Areas, the son of Callisto. (See Ursa Major.) 

JECevcules is represented as a warrior clad in the 
skin of the Nemaean lion, holding a club in his right 
hand and the dog Cerberus in his left. His foot is 
near the head of Draco, while his head lies 38° south, 
and his club reaches 10 degrees beyond. 

The principal star is Eas Algethi (a of Hercules 
and ^ of Serpentarius). This forms a triangle with 
(i and ^. A peculiar figure of four stars (-jr, t], ^, e), 
north of these, marks the body. (See Maps, Nos. 
5, 6, and 7.) The left knee is pointed out by ^, and 
the left foot by y. 

Mythological history. — This constellation immor- 
talizes the name of one of the greatest heroes of 
antiquity. Hercules was the son of Jupiter and 
Alcmena. While he was yet lying in his cradle, 
Juno, in her jealousy, sent two serpents to destroy 
him. The precocious infant, however, strangled 



258 THE SIDEEEAL SYSTEM. 

them with his hands. By the cunning artifice of 
Juno, Hercules was made subject to Eurystheus, his 
elder half-brother, and compelled to perform all his 
commands. Eurystheus enjoined upon him a series 
of the most difficult and dangerous enterprises which 
could be conceived. These are termed the " Twelve 
Labors of Hercules." Having completed these 
tasks, he afterward achieved others equally cele- 
brated. Near the close of his life he killed the cen- 
taur Nessus. The dying monster charged Dejanira, 
the wife of Hercules, to preserve a portion of his 
blood as a charm to use in case the love of her hus- 
band should ever fail her. In time, Dejanira thought 
she needed the potion, and Hercules having sent for 
a white robe to wear at a sacrifice, she steeped the 
garment in the blood of Nessus. No sooner had 
Hercules put on the fatal robe than the venom stung 
his bones and boiled through his veins. He at- 
tempted to tear it off, but in vain. It stuck to his 
flesh, and tore off great pieces of his body. The 
hero finding he must die, ascended Mount ^ta, 
where he erected a funeral pyre, spread out the skin 
of the Nemsean lion, and laid himself down upon 
it. Philoctetes applied the torch. With perfect se- 
renity of countenance Hercules awaited approaching 
death — 

" Till the god, the earthly part forsaken, 

From the man in flames asunder taken. 

Drank the heavenly ether's purer breath. 

Joyous in the new unwonted lightness 

Soared he upward to celestial brightness, 

Earth's dark, heavy burden lost in death." 

Schiller. 



EQUATOEIAL CONSTELLATIONS. 259 

(Map No. 6)— Fig. 78. 




Corona consists of six stars arranged in a semi- 
circular form. The brightest of these is Alphecca. 
This makes a triangle, with Mirac (e) and 6 in Bootes. 
It forms a similar figure with Mirac and Arcturus. 

Serpentariusy or Ophiuchus^ the serpent- 
bearer, is represented under the figure of a man 
grasping in both hands a prodigious serpent, which 
is writhing in his grasp. 

Prineipal stars. — Kas Alhagus (a), in the head, is 
of the second magnitude. It is about 5°fromEas 
Algethi, and forms a pair of stars conspicuous like 
the pairs in Gemini, Canis Minor, Canis Major, etc. 
(i marks the right shoulder, and fc the left. There is 



260 THE SIDEREAL SYSTEM. 

a small cluster near (3, called Taueus PonIatowskil 
An irregular square of four stars, near 7 Herculis, 
denotes the head of the serpent. 

Mythological history. — This constellation perpetu- 
ates the memory of ^sculapius, the father of medi- 
cine. He was so skilful that he restored several to 
life ; whereupon Pluto complained to Jupiter that 
his kingdom was in danger of being depopulated. 
Therefore Jupiter struck him with a thunderbolt, 
but afterward placed him among the constellations. 
Serpents were sacred to ^sculapius, because of the 
superstitious idea that thej have the power of re- 
newing their youth by" changing their skin. 

Libra represents the scales of Astrsea (Virgo), the 
goddess of justice. It may be recognized by the 
quadrilateral figure formed by its four principal 
stars. 

Scorpio is represented under the figure of a huge 
scorpion, stretching through 25°. It is a most in- 
teresting constellation. 

Frincipal stars. — Antares (a) is a fiery red star of the 
first magnitude. It marks the heart of the Scor- 
pion. The head is indicated by several stars, the 
most prominent of which is (3, arranged in a line 
sHghtly curved. The tail may be easily traced by a 
series of stars which wind around through the 
Milky Way in a very beautiful manner. 

Mythological history. — This is the scorpion tliat 
sprang out of the earth at the command of Juno, 
and stung Orion. Scorpio and Orion are so placed 



EQUATOBIAL CONSTELLATIONS. 261 

among the constellations that they never appear in 
the heavens together. 

Sagittarius, the archer, is represented as a cen- 
taur with his bow bent, as if about to let fly an 
arrow at Scorpio. 

Principal stars. — A row of stars from fjt- to /3 marks 
the bow : another from 7 eastward points out the 
arrow and the right arm drawn back in bending the 
bow. North of t, two stars of the fourth magnitude 
denote the head of the centaur. The " Milk Dipper j'' 
so called because the handle lies in the Milky Way, 
is a very striking figure. 

Mythological history. — This constellation is named 
in honor of Chiron, one of the centaurs. These 
monsters were represented as men from the head to 
the loins, while the remainder of the body was that 
of a horse — of which animal the ancients had so high 
an opinion that this union was not considered in the 
least degrading. Chiron was renowned for his skill 
in music, medicine, hunting, and the art of prophecy. 
The most distinguished heroes of mythology were 
among his pupils. He taught ^sculapius physic, 
Apollo music, and Hercules astronomy. At his 
death, the centaur furnished Dejanira with the in- 
formation which proved so fatal to Hercules. 

Capricornus contains no very conspicuous stars. 
The Southern Fish (No. 6) has one star of the first 
magnitude, Fomalhaut (a, No. 7), which on a clear 
summer evening may be seen skimming along the 
southern horizon. Antinous and the Eagle is a 



262 



THE SIDEREAL SYSTEM. 



double constellation. It contains a beautiful star 
of the first magnitude, Altair. This is conspicuous, 
as being the centre one in a row of three bright stars. 
A similar row, the first star of which is named ^, de- 
notes the tail of the eagle, the last star lying in Cerberus. 
The Dolphin is a beautiful little cluster in the form 
of a diamond. It is sometimes called " JoVs Coffin^ 

(Map No. 7)— Fig. 79. 




CygmiSi the swan, is a remarkable group of stars, 
the principal ones being so arranged as to form a 
large and beautiful cross. The upright piece lies 
along the Milky Way. It is composed of four stars, 
three of which, Deneb (a), 7, and /3, are bright, while 
the fourth is a variable star. In this constellation, 
No. 61, a minute star, scarcely visible to the naked 
eye, is noted as being the nearest to the earth of any 
of the fixed stars in the northern hemisphere. 



THE SOUTHERN CONSTELLATIONS. 263 

Lyrciy the harp, contains one brilliant blue star, 
Vega. Close by it is a parallelogram of four smaller 
stars, by which it may be easily recognized. This is 
the celestial lyre upon which Orpheus discoursed 
such ravishing music that wild beasts forgot their 
fierceness and gathered about him to listen, while 
the rivers ceased to flow, and the very rocks an .? 
trees stood entranced. 



THE SOUTHEKN CONSTELLATIONS 

CM.Q.x> No. 8)— Fig. 80. 




We now imagine ourselves viewing the stars visible 
only to a person south of the equator. The constel- 
lations are reversed with reference to the horizon. 
The two stars which, in the northern hemisphere, 



264 



THE SIDEREAL SYSTEM. 



compose the base of tlie parallelogram in Orion, 
form here the upper side. Sirius is above Orion. 
All the northern circumpolar constellations are 
hidden from view. At the southern pole there is no 
conspicuous star, but the richness and number of 
the neighboring stars compensate this deficiency, 
and give to the heavens an incomparable splendor. 
Here is the magnificent constellation Argo, in which 
we find Canopus, looked upon in ancient times as 

(Map No. 9)— Fig. 81. 




next to Sirius ia brilliancy : e, a variable star, now 
surpasses it in brightness. 

Nearly at the height of the south pole blazes the 
Southern Cross; below is the Centaur, containiag 
two stars of the first magnitude and five of the 
second ; and above is Hydrus, where shines Achernar, 
another beautiful star of the first magnitude. 



DOUBLE STABS. 265 

DOUBLE STAES, COLOEED STAES, 
NEBULA, ETC. 

Double Staes. — To the naked eye all the stars 
appear single. With the telescope, over 6,000 have 
been found to be double. Thus, Polaris consists of 
two stars about 18" apart, Eigel has a companion 
about 10" from it, and Sirius one distant 7". A good 
opera-glass will separate s Lyrse into two compo- 
nents. In case two stars happen to lie in the same 
straight line from us, though at immense distances 
from each other, their light will blend. They will be 
seen by the naked eye as a single star, and by the 
telescope as a double star. They are called optical 
double stars. Over 650, however, of the double stars 
have been found to be physically connected. Each 
double star of this class forms a biuary system of two 
suns revolving in an elliptical orbit about their com- 
mon centre of gravity, like the planets in the solar sys- 
tem, in accordance with Newton's law of gravitation. 
In a few instances there are combinations of triphf 
qicadruple, and even septuple stars. Thus e Lyrae is a 
double-double star, while ^ Orionis is a system of seven 
suns. The components of a double star commonly dif- 
fer in brightness ; so that frequently the fainter one 
is nearly lost in the brilliancy of its companion sun. 

The periods of some of these systems have been 
ascertained. Thus, Castor is a double star, and the 
two stars of which it is composed have performed 
an entire revolution about each other since they were 

12 



266 THE SIDEEEAL SYSTEM. 

discovered in 1780. ^ in tlie Great Bear lias a pe- 
riod of sixty-one years. In Berenice's Hair is a 
double star which traverses its orbit in fourteen 
years ; while one in Leo requires twelve centuries. 

Orbits. — It is not possible to estimate the dimen- 
sions of the orbits of the double stars, until their dis- 
tances from us are known. Taking the estimated dis- 
tance of 61 Cygni (550,000 times the sun's mean distance 
from the earth) as a basis, the companions of that 
system cannot cultivate a very intimate acquaintance, 
since they must be over a billion miles apart. From 
these data, astronomers have even attempted to cal- 
culate the mass of some of the double stars. 61 
Cygni, although scarcely visible to the naked eye, 
and known to be the second nearest to us of any of 
the fixed stars, is yet estimated to weigh one-third 
as much as our sun. 

CoLOEED Staes. — ^We have already noticed that the 
stars are of various colors. Sirius is white, Antares 
red, and CapeUa yellow ; while Ljnra has a blue tint^ 
and Castor a green one. In the pure transparent at- 
mosphere of tropical regions, the colors are far more 
briUiant. There, oftentimes, the nocturnal sky is a 
blaze of jewels, — the stars glittering with the green 
of the emerald, the blue of the amethyst, and the red 
of the topaz. In our latitudes, there are no stars 
visible to the naked eye which are decidedly blue or 
green. In the double and multiple stars, every 
color is presented in aU its richness and beauty. 
We find also combinations of colors complementary 
to each other. Here is a green star with a blood- 



VARIABLE STARS. 267 

red companion : here an orange and blue sun — there 
a yellow and purple one. The triple star y Andro- 
medse, is formed of an orange-red sun and two others 
of an emerald green. Every tint that blooms in the 
flowers of summer, flames out in the stars at night. 
" The rainbow flowers of the footstool and the starry 
flowers of the throne," proclaim their common 
Author ; while rainbow, flower, and star alike evince 
the same Divine love of the beautiful. 

As to the effects produced in a system having col- 
ored suns we can hardly conceive. Take a planet re- 
volving about 4^ Cassiopeia for instance. This is il- 
luminated by a red, a blue, and a green sun. Some- 
times, by the succession of these suns, a cheerful 
green day would present a charming relief to a 
fiery red one ; and that might be still further sub- 
dued by a gentle blue one. The odd contrasts of 
color and the vicissitudes of extreme heat and cold 
which obtain on such a world, present a picture 
which our fancy can sketch better than words can 
paint. The colors of the stars change. Sirius was 
anciently red. It is now unmistakably white. 
There are two double stars which were described by 
Herschel as white ; they are each now composed of 
a golden-yellow and a greenish star. 

Variable Stars. — These are stars which have pe- 
riodic changes of brilliancy. There are many of this 
class, of which the following are most conspicuous. 
Algol, in the head of Medusa, is a star of the second 
magnitude for about two and a half days, when it 
suddenly decreases, and in three and a half hours 



268 THE SIDEREAL SYSTEM. 

descends to tlie fourth magnitude. It then rekindles, 
and in three and a half hours again is as brilliant as 
ever. Miea, the wonderful, a star in the "Whale, has 
a period of eleven months. Its irregularities are 
very curious and fickle. It is ordinarily of the 
second magnitude 'for about fifteen days. It then 
decreases for three months, until it becomes in- 
visible even with a telescope. This period of dark- 
ness lasts five months; it then rebrightens for 
three months, until it regains its former lustre. Oc- 
casionly, however, it fails to brighten at all beyond the 
fourth magnitude, while on one occasion its light was 
almost equal to that of Aldebaran. Sometimes no 
perceptible change takes place for a month ; then 
again, there is a sensible alteration in a few days. 

The reason of this variability is not understood. 
It has been suggested, in the case of Mira, that it 
may be a globe revolving on its axis, and that dif- 
ferent portions of its surface, illuminated to different 
degrees of intensity, are thus presented to us. 
Others have conceived that there may be satellites 
revolving about these suns, and that when their dark 
bodies interpose between the stars and our earth, 
they ecHpse their light wholly or in part. 

Temporary Stars. — These are stars which sud- 
denly blaze out in the heavens, and then gradually 
fade away. The most celebrated one of this class 
burst forth in Cassiopeia, in the year 1572. Tycho 
Brahe says : " One night as I was examining the ce- 
lestial vault, I saw with unspeakable astonishment a 



TEMPOEARY STARS. 269 

star of extraordinary brightness in Cassiopeia. 
Struck with surprise, I could scarcely believe my 
eyes. To convince myself that there was no illusion, 
I called the workmen of my laboratory and the 
passers-by, and asked them if they saw the star 
which had so suddenly made its appearance." It was 
more brilliant than Sirius or Jupiter even, and could 
be compared only with Venus at her quadrature, ex- 
cept that it twinkled wonderfully. It was seen 
distinctly at midday. Its color was at first white, 
then yellow, and finally red. Its brightness decreased 
gradually until the spring of 1574, when the star dis- 
appeared from view and has not since been seen. 
As two brilliant stars had previously appeared in 
Cassiopeia, at intervals of about three centuries, 
they have been thought, by some, to be identical, 
and that it is only a variable star of long period. 

Since the discovery of Tycho Brahe, numerous in- 
stances are recorded of stars which have suddenly 
burst forth, and then either faded out entirely, or re- 
mained only as faint telescopic objects. In the latter 
case they are termed new stars. One of this kind 
appeared in Corona Borealis, in 1866. At first it was 
of the second magnitude, but in a week changed to 
the fourth, and in a month diminished to the 9th. 
Strangely, too, some stars have disappeared from 
the heavens, and are styled lost stars. These changes 
which are thus constantly taking place are calculated 
to make the term " eternal stars" seem a very in- 
definite phrase. 



270 THE SIDEEEAL SYSTEM. 

Exjplanation. — These phenomena are as yet little 
understood. A revolution about the axis would fail 
to explain the changes in color, besides being in it- 
seK a very unaccountable supposition. Some think 
that these stars revolve in enormous orbits of such 
eccentricity that at their most distant points they 
fade out of sight. Arago has shown, in reply to this, 
that for a star to decrease in brightness from the first 
magnitude to the second by simply moving directly 
from us, would require six years, even if it should 
speed away with the velocity of light. As we have 
just seen, the star of 1866 underwent this change in 
brilliancy in a week. 

The mind cannot help wonderiag if they are not 
instances of enormous conflagrations in which a 
world is overwhelmed in ruin ! The investigations 
of spectrum analysis indicate that the star of 1866 
consisted of hurning liydrogen gas. We can suppose 
that this was evolved by some convulsion, and taking 
fire, wrapped in flames the entire globe. This need 
not involve the idea of destruction, but only a change 
of form. In this manner a dark star may become 
luminous, or a bright one may be extinguished. 

Thus do we see that the process of apparent crea- 
tion and destruction is goiag on in the heavens imme- 
diately before the eye of the astronomer. New 
stars flash into hght, old stars are lost, worlds burst 
into flame, and their glowing embers fade into dark- 
ness. Are they re-created into new worlds? We 
know not. We only perceive that the same Al- 



STAE CLUSTERS. 



271 



mighty power whicli fitted up this earth for oui 
home is yet at work among the worlds about us, and 
we are thus witnesses of His eternal presence. 

Star Clusters. — These are groups of stars so 
massed together as to present a hazj, cloud-like ap- 
pearance. Several of them have been already 
named — the Pleiades, the Beehive in Cancer, Bere- 
nice's Hair, the Hjades, and the group in the sword- 
handle of Perseus. The stars of which they are 
composed can generally be easily distinguished by 

Fig. 82. 




STAR-CLUSTER IN TOUCAN. 



the naked eye, although by the use of a smaU opera 
or spy glass the number is largely increased. In 
the southern sky there are clusters still more re- 
markable. In the Cross is a group of 110 stars of 



272 THE SIDEEEAL SYSTEM. 

various colors, red, blue, and green, so that looking 
on it, says Herschel, is "like gazing into a casket 
of precious geras." A cluster in Toucan is compact at 
the centre, where it is of an orange-red color ; the 
exterior is composed of pure white stars, making a 
border of exquisite contrast. It is generally conceded . 
that there is some close physical relation existing 
between the stars composing such an " archipelago of 
worlds," but its nature is a mystery. They seem 
generally crowded together toward the centre, blend- 
ing into a continuous blaze of light. Yet, although 
they appear so densely compacted, it is probable 
that if we could change our stand-point, penetrating 
one of these groups of suns we should find it open- 
ing up and spreading out before us on our approach, 
until, in the midst, the suns would shine down upon 
us from the heavens as the stars do in our own sky. 
Nebula. — These are faint misty objects like specks 
of luminous clouds. They are generally either round 
or oval, and brightest at the centre. They differ 
from "clusters" in not being resolvable into stars 
when viewed through the largest telescopes. With 
the constant improvement made in these instru- 
ments, however, many nebulae have been resolved, 
and thus the number of clusters increased, while new 
nebulae are being discovered to take their places. 
Until of late, it was thought that all nebulae are 
simply groups of stars, which wiU be ultimately dis- 
cerned in the more powerful telescopes yet to be 
made. Spectrum analysis shows, however, that 



NEBULA. 273 

many of these luminous clouds are gaseous, and not 
solid. They cannot, therefore, be suns. Since they 
maintain the same position with respect to the stars, 
their distance must be inconceivably great, and in 
order to be visible to us, their magnitude must be pro- 
portionately vast. They are most abundant at the 
two poles of the Milky Way, but are more uniformly 
distributed over the heavens lying near the south 
pole. Those portions of the sky which are poorest 
in stars, are richest in nebulae. Herschel was ac- 
customed to say to his secretary, whenever for a 
brief time he saw no star passing the field of his 
telescope, as in the diurnal revolution the heavens 
swept by it, " Prepare to write ; nebulae are about 
to arrive." 

Nebulae are divided, according to their form, into 
six classes — elliptic^ annidar, spiral, 'planetary, irregu- 
lar nebulce, and nelmlous stars. 

The elliptic, or merely oval nebulae, are the most 
abundant. Under this head is commonly classed the 
" great nebula in Andromeda," which was discov- 
ered over a thousand years pig, 33. 
ago. It is visible to the naked 
eye. Prof. Bond, of the Cam- 
bridge Observatory, has part- 
ly resolved it into stars. He 
has distinctly counted 1500, 
although its nebulous appear- 
ance is still retained. Under 
fche telescope it is one of the nebula in andkomeda.. 

12* 




274 THE SIDEREAL SYSTEM. 

most glorious objects in the heavens. " If we sup- 
pose this nebula to be one continuous bed of stars 
of different sizes for its entire extent, it must 
comprise the enormous number of 30,000,000." The 
distance, of such nebulae from the earth entirely passes, 
pur comprehension. Some astronomers have estima- 
ted that a ray of light would require 800,000 years to 
span the gulf that intervenes. Imagination wearies 
itself in the attempt to understand these figures. 
They only teach us something of the limitless ex- 
panses of that space in which God is working the 
mysterious problem of creation. 

The annular nebulcE have the form of a ring. 
There are but four of these "ring universes." In 

Fis. 84. 




NEBULA IN LYRA. 



the cut is a representation of one in Lyra — first as 
seen by Herschel, and having in the centre a nebu- 
lous film nke a "bit of gauze stretched over a hoop ; " 
second, as shown in Lord Kosse's gTeat telescope, 
which resolves the filmy parts of the nebula into ex- 
cessively minute stars, and reveals a fringe of stars 




SriP.AT. CLUSTER IN CANES VENATICI. 



276 THE SIDEREAL SYSTEM. 

along the edge. Though apparently so small, its 
dimensions must be enormous. If no further from 
the earth than 61 Cygni, the diameter would be 
20,000,000 miles. It is, however, probably immensely 
further distant. 

The spiral or " whirlpool nebulae " are exceedingly 
curious in their appearance. The most remarkable 
one is that in Canes Yenatici. It consists of brilliant 
spirals sweeping outward from a central nucleus, 
and all overspread with a multitude of stars. One 
is lost in attempting to imagine the distance of such 
a mass, and the forces which produce such a " tre- 
mendous hurricane of matter — perhaps of suns." 

Planetary nebidoi, by their circular form and pale 
uniform light, resemble the disks of the most dis- 
tant planets of our system. Their edges are gener- 
ally Avell defined, though some- 
times slightly furred. Three- 
fourths of them are in the 
southern hemisphere. Several 
have a blue tinge. There is 
one in Ursa Major, which if lo- 
cated at the distance named 
before — that of 61 Cygni — 
would fill a space equal to 

PLANETARY NEBULA IN 

three times the entire orbit of pisces. 

Neptune. About twenty-five of these "island uni- 
verses" have been found scattered through the 
ocean of space. Columbus discovered a new^ conti- 
nent, and so immortalized his name ; what shall we 




NEBULA. 



277 



Fig. 87. 



say of the astronomer who discovers a universe oi 
worlds ? 

Irregular nehulce are those which have no definite 
form. Many of them present all the irregularities 
of clouds torn and 
rent by the tem- 
pest. Some of the 
hkenesses which 
may be traced by 
the fancy are 
strangely fantas- 
tic : for example, 
the " dumb-bell 
nebula" in the 
constellation Vul- 
pecula, and the 
"crab nebula" 
near the southern 
horn of Taurus. 




DUMB-BELL NEBULA. 



There is also one known as " the great nebula in the 
sword-handle of Orion," in which may be seen a 
faint resemblance to the wings of a bird. 

Nebulous stars are so called because they are en- 
veloped by a faint nebula, usually of a circular 
form. The star is generall}^ seen at the centre, al- 
though some which are elliptical surround two stars, 
one in each focus. It is thought that these may 
be suns possessing immense atmospheres, which are 
rendered visible somewhat as that of our sun is in 
the zodiacal light ; and that in like manner our sun 



278 the' sidereal system. 

Fig. 88. 




CRAB NEBULA. 

itself to those in space presents the appearance of 
a nebulous star. The luminous atmosphere of the 
star in Cygnus, if located at the distance of a Cen- 
tauri, is of an extent equal to " fifteen times the 
distance of Neptune fi'om the sun." 

Variable nebiilce. — Certain changes take place among 
the nebulae which can be accounted for only under 



NEBULA. 279 

the supposition that they, like some of the stars, are 
variable. Mr. Hind tells us of one in Taurus which 
was distinctly visible with a good telescope in 1852, 
but in 1862 it had vanished entirely out of the reach 
of a much more powerful instrument. It seems to 
have disappeared altogether. The great nebula in 
Argo, when observed by Herschel in 1838, had in 
the centre a vacant space containing a star of the 
first magnitude completely enshrouded by nebulous 
matter. In 1863, the nebulous matter had disap- 
peared, and the star was only of the sixth magni- 
tude. These facts as yet defy explanation. They 
only illustrate the vast and wonderful changes con- 
stantly taking place in the heavens. 

Doubh nebuke. — There seems to be a physical con- 
nection existing between some of the nebulae, similar 
to that already noticed in respect to certain stars. 
In the case of the latter, this inter-relation has been 
proved, since their movements even at their distances 
can yet be traced in the lapse of years. " But owing 
to the almost infinite depths in the abyss of the 
heavens at which these nebulae exist, thousands of 
years, perhaps thousands of centuries, would be 
necessary to reveal any movement." (GuUlemin.) 

Magellanic Clouds. — Not far from the southern 
pole of the heavens there are two cloud-like masses, 
distinctly visible to the naked eye, known to naviga- 
tors as " Cape Clouds." Sir John Herschel describes 
them as consisting of swarms of stars, clusters, and 
nebulae, seemingly grouped together in the wildest 



280 THE SIDEEEAL SYSTEM. 

confusion. In the larger, lie found 582 single stars, 
46 clusters, and 291 nebulae. 

The Milky Way — Via Lactea or Galaxy, as it is 
variously termed — is that luminous, cloud-like band 
that stretches across the heavens in a great circle. 
It is inclined to the celestial equator about 63°, and 
intersects it in the constellations Cetus and Yirgo. 
This stream of suns is divided into two branches 
from a Centauri to Cygnus. To the naked eye it 
presents merely a diffused light ; but with a power- 
ful telescope it is found to consist of myriads of stars 
densely crowded together. These stars are not uni- 
formly distributed through its entire extent. In 
some regions, within the space of a single square 
degree we can discern as many as can be seen with 
the naked eye in the entire heavens. In other parts 
there are broad open spaces. A remarkable instance 
of this occurs near the Southern Cross. There is a 
dark pear-shaped vacancy with a single bright star 
at the centre, glittering on the blue background of 
the sky. In viewing it, one is said to be impressed 
with the idea that he is looking through an opening 
into the starless depths beyond the Milky Way. 

The number of stars in the galaxy which may be 
seen by Herschel's great reflector is estimated at 
twenty-one and a half millions. With the more 
powerful instruments now being made it is probable 
the number will be largely increased. The northern 
galactic pole is situated near Coma Berenices, and 
the southern in Cetus. Advancing from either pole 



THE MILKY WAY. 281 

toward the Milky Way, the number of stars increases, 
at first slowly and then more rapidly, until the pro- 
portion at the galaxy itself is thirty-fold. 

Hersclid's theory. — Sir W. Herschel has conjec- 
tured that the stars are not indifferently scattered 
through spac@, but are collected in a stratum some- 
thing like that shown in the cut, and that our sun 

Fig. 89. 




HEESCHEL'S THEORY OF THE MILKY WAY. 

occupies a place at S, near where the stream branches. 
A and E are the galactic poles. It is evident that, 
to an eye viewing the stratum of stars in the direc- 
tion SB, SC, or SD, they would seem much denser 
than in the direction SA or SE. Thus are we to 
think of our own sun as a star of the second or third 
magnitude, and our little solar system as plunged 
far into the midst of this vortex of Avorlds, a mere 
atom along that 

" Broad and ample road 
Whose duet is gold and pavement stars." 



282 THE SIDEREAL SYSTEM. 

Nebulae Hypothesis. — Tins is a theory which was 
advanced by Laplace, to show how the solar system 
was formed. In the "beginning," all the matter 
which now composes the sun and the various planets, 
with their moons, was in a gaseous and highly heated 
state. It filled all the space now occupied by the 
system, and extended far beyond the orbit of Nep- 
tune. In other words, the solar system was simply 
an immense nebula. The heat, which- is the repel- 
lant force, overcame the attraction of gravitation 
Gradually the mass cooled by radiation. As centu- 
ries passed, the repellent force becoming weaker, the 
attractive force drew the matter and condensed it 
toward one or more centres. The nebula then 
presented the appearance of a nebulous star — a 
nucleus enveloped to a great distance by a gaseous 
atmosphere. According to a well-known law in 
philosophy, seen in every-day life, in a whirlpool, 
a whirlwind, or even in water poured into a funnel, 
wherever matter seeks a centre, a rotary motion is 
established. As this rotary motion increased, the 
centrifugal force finally overcame at the exterior the 
attraction of gravitation, and so threw off a ring of 
condensed vapor. Centuries elapsed, and again, un- 
der the same conditions, a second ring was detached. 
Thus, one by one, concentric rings were separated 
from the parent nebula, all revolving in the same 
plane and in the same direction. These different 
rings, becoming gradually consolidated, formed the 
planets, — generally however, in this process, while 



NEBULAE HYPOTHESIS. 283* 

still in the vaporous state and slowly condensing, 
themselves throwing off rings which were in turn 
consolidated into satelHtes. In the case of Saturn, 
several of these secondary rings did not break up, 
and so condense into globes, but still remain as 
rings which revolve about the planet.* Mitchell 
naively remarks, "Saturn's rings were left un- 
finished to show us how the world was made." 
The ring which formed the minor planets broke up 
into small fragments, none large enough to attract 
the rest and thus form a single globe. The central 
mass of vapor finally condensed itself into the sun, 
which remains the largest member of the system. 
According to this theory, the sun may yet give off 
a few more planets, whose orbits will not exceed its 
present diameter. After a time its heat will have all 
been radiated into space, its fire will become extinct, 
and life on the planets will cease. We know not 
when this remote event may occur. "We cannot 
fathom the purpose of God in creating and main- 
taining this system of worlds, nor foretell how soon it 
may complete its mission. We are assured, however, 

" That nothing walks with aimless feet, 
That not one life shall be destroyed, 
Or cast as rubbish to the void. 
When God hath made the pile complete." 

In Memoriam. 

* It is possible that these rings may yet break up and form 
new satellites for that planet Indeed, some hold that ou(^ at 
least of the rings has thus been resolved into small meteorites. 
These may be attracted, and so picked up, one by one, by the larger 
in succession, until they form another moon, which will continue 
to revolve about the planet as the ring does now. 



284 



THE SIDEREAL SYSTEM. 
Fig. 90. 




CELESTIAL CHEMISTEY. 

Spectrum Analysis. — The rainbow — that child of 
the sun and shower — is familiar to aU. The brilliant 
band of colors, seen when the sunbeam is passed 
through a prism, is scarcely less beautiful. The ray 
of light containing the primary colors is spread out 
fan-Hke, and each tint reveals itself. This variously 
colored band is called in philosophy a spectrum (plu- 
ral, spectra). There are three different kinds of 
spectra — 

1st. When the light of a solid or liquid body, as 



CELESTIAL CHEMISTRY. 285 

iron white-hot, is passed through a prism, the spec- 
trum is continuous^ and consists of a series of distinct 
colors, varying from red on one side to violet on the 
other. 

2d. If the light of a burning gas containing any 
volatilized substance be passed through a prism, the 
spectrum is not continuous, but is ornamented by 
bright-colored lines— -sodium giving two yellow 
lines, strontia a red one, silver two beautiful green 
ones. Each element produces a definite series 
which can be readily recognized as its test. 

3d. If a light of the first kind be passed through 
one of the second, the spectrum will be found to be 
crossed by darh lines. Thus, if the white light of a 
burning match be passed through a flame containing 
sodium, instead of the vivid yellow fines so charac- 
teristic of that metal, two black lines will exactly 
occupy their place. A gaseous flame absorbs the rays 
of the same color that it emits. 

The Specteoscope. — This instrument consists of 
two small telescopes, with a prism mounted between 
their object-glasses, in the manner shown in the cut. 
The rays of light enter through a narrow sHt at A 
and are rendered parallel by the object-glass. They 
then pass through the prisms at 0, are separated into 
the different colors, and entering the second telescope 
at D, fall upon the eye at B. A third telescope is 
sometimes attached, which contains a minutely accu- 
rate scale for measuring the distances of the lines. In 
addition, a mirror may throw in a ray of sunlight or 



286 THE SIDEREAL SYSTEM. 

starlight at one side of the slit, and so we can com- 
pare the spectrum of the sunbeam with that of any 
flame we desire. 

Fig. 91 




A BFECTBOSCOPE. 



Revelations of the spectroscope concerning the sun, — 
The spectrum of the sunbeam is not continuous, but 
is crossed by a large number of dark lines, called, 
from their discoverer, Fraunhofer's lines. It is there- 
fore concluded that the sun's light is of the third 
class just named, and that it is produced by the vivid 
light of a highly heated body shining through a 
flame full of volatilized substances. But not only 
does spectrum analysis thus shed light on the phys- 
ical constitution of the sun, but these lines are so 
distinctive, so marked and varied, that the very ele- 
ments of which the sun is composed may be dis- 
covered. Thus, for example, iron gives a spectrum 
of some 70 lines, differing in intensity and relative 
length. These are bright when iron vapor is bum- 



CELESTIAL CHEMISTRY. 287 

ing, and dark when white light is passed through 
such burning vapor. In the solar spectrum we have 
the perfect coincidence of 70 dark lines, line for line 
and strength for strength. The conclusion is irre- 
sistible that iron is contained in the sun's atmos- 
phere. The following include all the elements that 
are now known to exist in it : 



Sodium, 


Iron, 


strontium 


Calcium, 


Chromium, 


Cadmium, 


Barium, 


Nickel, 


Cobalt, 


Magnesium, 


Zinc, 


Hydrogen. 



Staks aee Suns. — The same method of analysis 
has been applied to the stars. Their spectra also 
are marked by dark lines. Their constitution is 
therefore like our sun ; they contain also the same 
familiar elements. Aldebaran seems the most like 
our earth. It has at least nine elements known to 
chemists : 



Sodium, 


Iron, 


Magnesium, 


Hydrogen, 


Bismuth, 


Antimony, 


Tellurium, 


Mercury, 


Calcium. 



Betelgeuse contains many elements known to us, 
but no hydrogen. — ^What a world that must be with- 
out water ! Arcturus, Kutherford says, closely re- 
sembles our sun. 

We thus trace in the faintest star that trembles in 
the measureless depths of space the same elements 
that compose the food we eat and the water we 
drink. We know that we are akin to nature every- 
where — that we are a part of a system vast as the 
universe. 



288 THE SIDEEEAL SYSTEM. 

Spectea of Nebula. — Instead of being marked 
with dark liaes, as are the spectra of the stars, many 
of these exhibit bright lines. Their spectra are con- 
tinuous. This proves the nebula to consist, not, like 
the stars, of an intensely heated solid body shining 
through aluminous atmosphere, but of a glowing mass 
of gas. Out of 60 nebulse examined by Mr. Huggins, 
20 exhibited the bright lines belonging to the gases, 
and all contained nitrogen. 

It is possible in this manner even to decide the 
relative brightness of the different nebulae. The 
dumb-bell nebula was found to emit a light only 
about one twenty-thousandth part that of a common 
wax-candle. If this matter be a "sim-germ," how 
immensely must it become condensed before its 
rushlight gHmmering can rival the dazzling brilliancy 
of even our own sun! 

The Solae Flames, which before were seen only 
at an eclipse, can now be examined at any time. 
The sun is a sea of fire. Flames travel over its sur- 
face faster than the earth in its orbit : one shot out 
80,000 miles and disappeared in ten minutes. Such 
tremendous convulsions surpass all terrestrial phe- 
nomena. 

TIME. 

SiDEEEAL Time. — A sidereal day is the exact in- 
terval of time in which the earth revolves on its axis. 
It is found by marking two successive passages of a 
star across the meridian of any place. This is so 



TIME. 289 

absolutely uniform, that the length of the sidereal 
day has not varied y^ of a second in 2,000 years, 
The sidereal day is divided into twenty-four equal 
portions, which are called sidereal hours, and each 
of these into sixty portions, termed sidereal min- 
utes, etc. 

Astronomical clocks are regulated to keep sidereal 
time. The day commences when the vernal equinox 
is on the meridian. Therefore, the time by the si- 
dereal clock does not in any way point out the hour 
of the ordinary day. It only indicates how long it 
is since the vernal equinox crossed the meridian, and 
thus always shows the right ascension of any star 
which 'may happen to be on the meridian at that 
moment. The hours of the clock are easily reduced 
to degrees (see p. 38). The astronomer always 
reckons the hours of the day consecutively up to 
twenty-four. 

SoLAE Time. — A solar day is the interval between 
two successive passages of the sun across the me- 
ridian of any place. If the earth were stationary in 
its orbit, the solar day would be of the same length 
as the sidereal ; but while the earth is turning around 
on its axis, it is going forward at the rate of 360° in 
a year, or about 1° per day. When the earth has 
made a complete revolution, it must therefore per- 
form a pai*t of another revolution through this ad- 
ditional degree, in order to bring the same meridian 
vertically under the sun. One degree of diurnal 
revolution is about equal to four minutes of time. 

13 



290 THE SIDEREAL SYSTEM. 

Hence the solar day is about four minutes longer 
tlian the sidereal day. For the convenience of so- 
ciety, it is customary to call the solar day 24 hours 
long, and make the sidereal day only 23 hr. 56 min. 
4 sec. in length, expressed in mean solar time. A 
sidereal day being shorter than a solar one, the si- 
dereal hours, minutes, etc., are shorter than the 
solar ; 24 hours of mean solar time being equal to 
24 hr. 3 min. 56 sec. of sidereal time. 

From what has been said, it follows that the earth 
makes 366 revolutions around its axis in 365 solar 
days. 

Mean Solae Time. — The solar days are of unequal 
length. To obviate this difficulty, astronomers sup- 
pose a mean sim moving through the equator of the 
heavens (which is a circle and not an ellipse) with a 
perfectly uniform motion. When this mean sun 
passes the meridian of any place, it is mean noon ; 
and when the true sun is in the same position, it is 
apparent noon. This day is the average length of all 
the solar days in the year. The clocks in common 
use are regulated to keep mean time. When, there- 
fore, it is twelve by the clock, the sun may be either 
.a little past or a little behind the meridian. The 
difference between the sun-time (apparent solar- 
time) and the clock-time (mean time), is called the 
" equation of time."" This is the greatest about the 
first of November, when the sun is sixteen and a 
quarter minutes in advance of the clock. The sun 
is the slowest about February 10th, when it is about 



TIME. 291 

fourteen and a half minutes behind mean time. 
Mean and apparent time coincide four times in the 
year — namely, April 15th, June 15th, September 1st, 
and December 24th. On those days the noon-mark 
on the sun-dial coincides with twelve o'clock. In 
France, until 1816, apparent time was used ; and the 
confusion was so great, that Arago relates how the 
town clocks would differ thirty minutes in striking the 
same hour. As the time varied every day, no watch- 
maker could regulate a watch or clock to keep it. 

The Sun-dial — The apparent time of the dial may 
be readily changed to mean time, by adding or sub- 
tracting the number of minutes given in the almanac 
for each day in the year, under the heading " sun 
slow" or "sun fast." As a noon-mark is thus a 
very convenient method of regulating a timepiece, 
especially in the country, the following manner of ob- 
taining one without a transit instrument may be 
useful. 

Select a level hard surface which is exposed to the 
sun from about 9 A. M. to 3 p. m. Upon this describe, 
with a pair of compasses, a circle of eight or ten 
inches in diameter. Take a piece of heavy wire, six 
or eight inches in length, one end of which is 
sharpened. Drive this perpendicularly into the cen- 
tre of the circle, leaving it just high enough to allow 
the extreme end of its shadow to fall upon the circle 
about 9 J or 10 A. m. Mark this point, and also the place 
where the shadow touches the circle in the afternoon. 
Take a point half-way between the two, and drawing 



292 



THE SIDEBEAL SYSTEM. 



a line from that to the centre of the circle, it will 
be the meridian line or noon-mark. 

Why the solae days aee of iinequal length. — 
There are two reasons for this — the unequal orbital 
motion of the earth and the obliquity of the ecHptic. 
Fkst : the orbit of the earth is an ellipse ; and thus 
the apparent yearly motion of the sun along the 
ecliptic is variable. In perihelion, in January, the 
sun appears to move eastward daily 1° 1' 9.9" ; while 
at aphelion, in July, only 57' 11.5". As the earth 
in its diurnal motion revolves uniformly from west to 
east, and the sun passes eastward irregularly, this 
must produce a corresponding variation in the 
length of the solar day. The sun, therefore, comes 
to the meridian sometimes earlier and sometimes 
later than the mean noon, and they agree only at 
perihelion and aphelion. 

Second : as we have just seen, the mean sun is sup- 
posed to move in a circle and not an ellipse. This 
would make 
the motion 
along the 
ecliptic uni- 
form, but the 
obliquity of 
the ecliptic 
would still 
ir- 




M L K 



q P O N 

cause an ir- 
regularity in the length of the day. The mean sun 
is therefore supposed to pass along the equinoctial, 



TIME. 293 

which is perpendicular to the earth's axis ; while the 
ecliptic is inclined to it 23° 28'. Let A represent the 
vernal equinox, I the autumnal, AEI the ecliptic, 
AI the equinoctial, PK, PL, PM, etc., meridians. 
Let the distances AB, BC, CD, etc., be equal arcs of 
the ecliptic, which are passed over by the sun in 
equal times. Next, mark off on the equinoctial dis- 
tances Aa, ab, be, etc., equal to AB, BO, etc. These 
are equal arcs of right ascension, or hour-circles, 
through which the earth, revolving from west to east, 
passes in equal times. Now, meridians drawn through 
these divisions, would not agree with those drawn 
through equal divisions on the ecliptic. Hence, a sun 
moving along the echptic, which is inclined, would not 
make equal days, even though the ecliptic were a per- 
fect circle. Let us see how the mean and apparent 
solar days would compare. Let the real sun pass in 
its eastward course from A to B in a certain time, the 
mean sun moving the same distance would reach the 
point a, since the latter travels on the base and tho 
former the hypothenuse of a triangle. The earth, re- 
volving from west to east, would cause the real sun 
to cross any meridian earlier than the mean sun ; 
hence, apparent time would be faster than clock-time. 
By holding the figure up above us toward the 
heavens, we can see how a westerly sun would cross 
the meridian earlier than an easterly one. Follow- 
ing the same reasoning, we can see that at the sol- 
stice, solar and mean time would agree ; while 
beyond that point the mean time would be faster. 



294 THE SIDEREAL SYSTEM. 

The Ciyil Day. — This is the ,mean solar day of 
which we have spoken. It extends from midnight 
to midnight. The present method of dividing the 
day into two portions of twelve hours each, was 
adopted by Hipparchus, 150 years b. c, and is now 
in general use over the civilized world. Until re- 
cently, however, very many nations terminated one 
day and commenced the next at sunset. Under this 
plan, 10 o'clock on one day would not mean the same 
as 10 o'clock on another day. The Puritans com- 
menced the day at 6 p. M. The Babylonians, Per- 
sians, and modern Greeks begin the day at sunrise. 
The names of the days now in use are derived as 
follows : 



1. Dies Solis (Latin) 

2. Dies Lunse ( " ) 

3. Tins daeg (Saxon) 

4. Wodnes daeg...( " ) 

5. Ttiurnes daeg . . ( " ) 

6. Friges daeg ( " ) 

7. Dies Saturni . . . ( Latin ) 



...Sun's day. 
...Moon's day. 
. ..Tins' s day. 
...Woden's day. 
. ..Tiior's day. 
...Friga's day. 
...Saturn's day. 



The Tear. — The sidereal year is the interval of a 
complete revolution of the earth about the sun, meas- 
ured by a fixed star. It comprises 365 d., 6 hrs., 
9min., 9.6 sec. of mean solar time. The mean solar 
year (tropical year) is the interval between two suc- 
cessive passages of the sun through the vernal equi- 
nox. It comprises 365 d., 5 hrs., 48min., 49.7 sec. 
If the equinoxes were stationary, there would be no 
difference between the sidereal and tropical year. 
As tlie equinoxes retrograde along the ecliptic 50" of 
space annually, the former is 20 min., 20 sec. longer. 



TIME, 295 

The anomalistic year is the interval between two 
successive passages of the earth through its perihe- 
lion. It is 4min., 40sec. longer than the sidereal 
year. 

The Ancient Yeak. — The ancients ascertained 
the length of the year by means of the gnomon. This 
was a perpendicular rod standing on a smooth plane 
on which was a meridian line. When the shadow 
cast on this line was the shortest, it indicated the 
summer solstice ; and when it was the longest, the 
winter solstice. The number of days required for 
the sun to pass from one solstice back to it again de- 
termined the length of the year. This they found 
to be 365 days. As that is nearly six hours less than 
the true solar year, dates were soon thrown into con- 
fusion. If, at a certain date the summer solstice oc- 
curred on the 20th June, in four years it would fall 
on the 21st ; and thus it would gain one day every 
four years, until in time the summer solstice would 
happen in the winter months. 

JuLMN Calendar. — Julius Caesar first attempted 
to make the calendar year coincide with the motions 
of the sun. By the aid of Sosigenes, an Egyptian 
astronomer, he devised a plan of introducing every 
fourth year a leap-year, which should contain an 
extra day. This was termed a bissextile year, since 
the sixth (sextilis) day before the kalends (first day) 
of March was then counted twice. 

Geegoeian Calendar. — Though the Julian calen- 
dar was nearly perfect, it was yet somewhat defec- 



296 THE SIDEEEAL SYSTEM. 

tive. It considered the year to consist of 365^ days, 
wMcli is 11 min. in excess. This accumulated year 
by year, until in 1582 the difference amounted to 
ten days. In that year, the yernal equinox occurred 
on the 11th of March, instead of the 21st. Pope 
Gregory undertook to reform the anomaly, by drop- 
ping ten days from the calendar and ordering that 
thereafter only centennial years which are divisible 
by 400 should be leap-years. The Gregorian calen- 
dar was generally adopted in all Catholic countries. 
Protestant England did not accept the change until 
1752. The difference had then amounted to 11 days. 
These were suppressed and the 3d of September 
was styled the 14th. 

Dates reckoned according to the Julian calendar 
are termed Old Style (O. S.), and those according to 
the Gregorian calendar New Style (N. S.) This 
sweeping change was received in England with great 
dissatisfaction. Prof. De Morgan narrates the fol- 
lowing. "A worthy couple in a country town, scandal- 
ized by the change of the calendar, continued for 
many years to attempt the observance of Good Fri- 
day on the old day. To this end they walked seri- 
ously and in full dress to the church door, on which 
the gentleman rapped with his stick. On finding no 
admittance, they walked as seriously back again and 
read the service at home. There was a wide-spread 
superstition that, when Christmas day began, the 
cattle fell on their knees in their stables. It was as- 
serted that, refusing to change, they continued their 



TIME. 297 

prostrations according to tiie Old Style. In Eng- 
land, the members of the government were mobbed 
in the streets by the crowd, which demanded 
the eleven days of which they had been illegally 
deprived." 

Commencement of the Year. — The Jews began 
their civil year with the autumnal equinox, but their 
ecclesiastical with the vernal. When Caesar revised 
the calendar, among the Romans the year com- 
menced with the winter solstice (Dec. 22), and it is 
probable he did not intend to change it materially. 
He, however, ordered it to date from January 1st, in 
order that- the first year of his new calendar should 
begin with the day of the new moon immediately 
succeeding the winter solstice. 

The Earth our Timepiece. — The measure of time 
is, as we have just seen, the length of the mean 
day. That is estimated from the length of the si- 
dereal day. Hence the standard for time is the rev- 
olution of the earth on its axis. All weights and 
measures are based on time. An ounce is the weight 
of a given bulk of distilled water. This is measured 
by cubic inches. The inch is a definite part of the 
length of a pendulum which vibrates seconds in the 
latitude of London. Arago remarks, a man would 
be considered a maniac who should speak of the in- 
fluence of Jupiter's moons on the cotton trade. Yet 
there is a connection between these incongTuous 
ideas. The navigator, travelling the waste of waters 
where there are no paths and no guide-boards, may 



298 



THE SIDEEEAL SYSTEM. 



reckon liis longitude by tlie eclipses of Jupiter's 
moons, and so decide the fate of his voyage. We 
can easily see how the revolution of the earth on its 
axis influences the cost of a cup of tea. 



CELESTIAL MEASUEEMENTS. 

Many persons read the enormous figures which 
indicate the distances and dimensions of the heaven- 
ly bodies with an indefinite idea, which conveys no 
such feeling of certainty as is experienced when 
they read of the distance between two cities, or the 
number of square miles in a certain State. Many, 
too, imagine that celestial measurements are so mys- 
terious in themselves that no common mind can 
hope to grasp the methods. Let us attempt the so- 
lution of a few of these problems. 

1st. To FIND THE DISTANCES OF THE PLANETS FEOM 

THE SUN. — Li the figure, E represents the earth, ES 
the earth's distance from 
the sun, Y the planet Ye- 
nus, and YES the angle of 
elongation (a right-angled 
triangle). It is clear, that 
as Yenus swings apparent- 
ly east and west of the sun, 
this angle may be easily 
measured ; also, that it will 
be the greatest when Yenus 
is in aphehon and the earth 



Fig. 93. 




COMPARATIVE DISTXSCE OV VENUa 
ANDTHEEABTH. 



CELESTIAL MEASUBEMENTS. 299 

in perihelion at the same time, for then YS will be 
the longest and YE the shortest. Now in every 
right-angled triangle the proportion between the 
hypothenuse, ES, and the side opposite, YS, changes 
as the angle at E varies, but with the same angle re- 
mains the same whatever may be the length of the 
lines themselves. This proportion between the hy- 
pothenuse and the side opposite any angle is termed 
the sine of that angle. Tables are published which 
contain the sines for all angles. In this way, the 
mean distance of Yenus is found to be 3^* that of 
the earth. Mars f times, Jupiter 5^ times, etc. 

The. same result would be obtained by the use of 
Kepler's third law ; and on page 29, we saw how 
the distances of the planets themselves could be de- 
termined by the periodic times, if the distance of 
the earth from the sun is first known. So that 
when we have accurately determined the sun's dis- 
tance from us, we can then decide by either of the 
methods named the distance of all the planets. In- 
deed that is, as already remarked, the " foot-rule" 
for measuring all celestial distances. 

2d. To MEASURE THE MOON'S DISTANCE FROM THE 

EARTH. — (1.) The ancient method. — As the moon's dis- 
tance is so much less than that of the other heavenly 
bodies, it is measured by the earth's semi-diameter. 



* If the pupil has studied Trigouometiy, he may appl}^ here 
the simple proportion — 

ES : VS : : Radios : Sine of 47° 15'^ = greatest elongation of Vonus. 



300 THE SIDEREAL SYSTEM. 

The metliod, an extremely rougli one, which was in 
use among the ancients, was something like the fol- 
lowing. In an eclipse of the moon, that body passes 
through the earth's shadow in about four hours. If, 
then, the moon travels along its orbit in four hours 
a distance equal to the diameter of the earth, in 
twenty-four hours it would pass over six times, and 
in a lunar month (about thirty days) one hundred 
and eighty times, that distance. The circumference 
of the lunar orbit must be then one hundred and 
eighty times the diameter of the earth. The ancients 
supposed the heavenly orbits to be circles, and as 
the diameter of a circle is about ^ of the circum- 
ference, they deduced directly the diameter of the 
moon's orbit as 120 times, and the distance of the 
the moon from the earth as 60 times the semi-diam- 
eter of the earth. 

(2.) Modern method by the lunar parallax. — Under 
the liead of parallax we saw how, in common life, 
we obtain a correct idea of the distance of an object 
by means of our two eyes. We proved that one eye 
alone gives no notion of distance. Just, then, as we 
use two eyes to find how far from us an object is, so 
the astronomer uses two astronomical eyes or obser- 
vatories, located as far apart as possible, to find the 
parallax of a heavenly body. In the figure, M rep- 
resents the moon, G an observatory at Greenwich, 
and C another at the Cape of Good Hope. At the 
former, the distance from the north pole to the 
centre of the moon, measured on a meridian of the 



CELESTIAL MEASUBEMENTS. 



301 



celestial sphere, is found to be 108°. At the latter 
station, the distance from the south pole to the 
moon's centre is measured in the same way, and 
found to be 73J°. The sum of these angles is 181^°. 
Now, the entire distance from the north pole around 
to the south pole, measured on a meridian, can be 
only half a great circle, or 180°. This difference of 



Pig. 94. 




MEASURING MOON'S DISTANCE FROM THE EARTH. 



1|° must be the difference in the position of the 
moon, as seen from the two observatories. For the 
observer at the former station will see the moon 
projected on the celestial sphere at G', and in meas- 
uring its distance from the north pole wiU measure 
an arc hG' further than if he were located at E, the 
centre of the earth. The observer at the latter sta- 
tion will see the moon projected on the celestial 
sphere at C, and in measuring its distance from the 



302 THE SIDEREAL SYSTEM. 

south pole will measure an arc hO' more than if he 
were located at E, the centre of the earth. The sum 
of &G' and hC = G'C is the difference in the position 
of the moon as seen from the two stations. In other 
words, it is the moon's parallax. The arc GC 
measures the angle C'MG'; that angle is equal to 
the opposite angle GMC = 1J°. Now, in the four- 
sided figure GECM, the sides GE and CE are each 
equal radii of the earth = 3956 miles; while the dis- 
tance from G to C is the difference in the latitude of 
the two places. The angles ZGM and Z'CM, being 
the zenith distances of the moon, are known, and so 
the angles MGE and MCE are easily found. EM, 
the moon's distance from the centre of the earth, is 
thus readily computed by a simple trigonometrical 
formula. 

(3.) The Tiorizontal parallax of the moon is most com- 
monly found by estimating its distance, not from the 
north and south poles, as just explained under the 
general meaning of the term parallax, but from a 
fixed star. The moon's horizontal parallax is now 
estimated at 57', which makes its distance about 
sixty times the earth's semi-diameter.'^ 

To FIND THE sun's DISTANCE FROM THE EARTH, — 

This might be estimated by obtaining the solar 

* In figure 95, let S represent tlie moon, sun, or any other 
heavenly body, AB the semi-diameter of the earth, and ASB the 
" horizontal parallax" of the body. Then, by the following trig- 
onometrical foimula, the distance from the earth may be easily 

calculated — 

AS : AB : : Radius : Sin of ASB. 



CELESTIAI. MEASUREMENTS. 303 

• 

parallax in the same manner as the lunar parallax. 
It would be only necessary to take the sun's distance 
from the north and south poles respectively at 
Greenwich and the Cape of Good Hope, and then 
subtracting 180° from the sum of the two angular 
distances, the remainder would be the solar parallax. 
The difficulty in this method lies in the fact that 
when the sun shines the air is full of tremulous mo- 
tion. This increases refraction — that plague of all 
astronomical calculations — to such an extent that it 
becomes impossible to calculate so small an angle 
with any accuracy. Neither can the parallax be 
estimated, as in the case of the moon, by measuring 

Fig. 96. 




the distance from a fixed star, since when the sun 
shines the stars near by are invisible even in a tele- 
scope. Astronomers have therefore been compelled 
to resort to other methods. 

(1.) Calculation of solar parallax by observation of 
the planet Mars. — We have already seen that the dis- 
tance of Mars from the sun is 4 that of the earth 
fi-om the sun. If, therefore, we can find Mars' dis- 
tance from the earth, we can multiply it by three, 



304 THE SIDEREAL SYSTEM. 

and so obtain the distance of the snn from the earth. 
In 1862, when Mars was in opposition, it came very 
near us, for it was in perihelion while the earth was 
in aphehon, so that its distance (as since ascertained) 
was only 126,300,000 - 93,000,000 = 33,300,000 miles. 
Observers at Greenwich ai d the Cape, and at various 
American and European observatories, calculated 
the distance of the planet from the north and south 
poles, as well as from several fixed stars, in precisely 
the manner just explained for obtaining the lunar 
parallax. The result of these observations fixed the 
solar parallax at S.94:".^ 

(2.) Calculation of solar parallax by ohservatioii of 
the transit of Venus. — In the figure, let A and B rep- 
resent the positions of two observers stationed at 

Fig. 96. 



TEANSIT OF VENXTS. 

opposite sides of the earth. At the time of the 
transit, the one at A will see the planet Yenus as a 
round black spot at Y" on the sun's disk, while the 
one at B will see it at Y'. The distance Y'Y" is the 

* By the formula on page 302, we have — 

AS : AB : : Radius : Sin S.W. 



CELESTIAL MEASUREMENTS. 305 

difference in the position of Yenus as seen from tlie 
two stations on the earth. The distance AB is the 
diameter of the earth. The distance Y'V" is as much 
greater than AB as YV" is greater than YA. The 
distance of Yenus from the sun is known, by Prob. I., 
to be .72 that of the earth. The distance of Yenus 
from the earth must be, then, 1.00 — .72 = .28. 
Hence, YY", the distance from the sun to Yenus, = 
.72 -^ .28 = 2.5 times the length of AY, the distance 
of Yenus from the earth. Therefore, Y'Y" is equal 
to 2 J times AB, the earth's diameter, or 5 times: 
the solar parallax. Knowing the hourly motion of 
Yenus, it is only necessary for each observer to find 
when the planet's shadow enters upon and leaves the 
sun's disk to determine the length of the path (chord) 
it traces. A comparison of the length and direction 
of these chords will give the length of Y' Y" in 
seconds of space. 

The advantage of this method is, that as the dis- 
tance Y' Y" is ^-ve times that of AB, an error in meas- 
uring that chord affects the solar parallax less than 
one-fifth. 

Time of a transit of Venus. — This is an event of rare 
occurrence. It happens only at intervals of 8, 105 1 ; 
8, 121 J, years, &c. Were the planet's orbit in the same 
plane as the ecliptic, a transit would take place dur^ 
ing each synodic revolution ; but as it is inclined 
about 3^°, the transit can occur only when the earth 
is at or near one of the nodes at the same time with 
the planet, when ia inferior conjunction. As the nodes 



306 THE SIDEREAL SYSTEM. 

of Yenus fall in that part of the earth's orbit which 
we pass in the beginning of June and December, 
transits always occur in those months. 

The transit of June 3d, 1769, excited great interest. 
King George III. fitted out an expedition to Tahiti, 
under the command of the celebrated navigator Capt. 
James Cook. In order to make the angle as great 
as possible, and so increase the length of the chords, 
or paths of the shadow across the sun, astronomers 
were sent to all the most favorable points of obser- 
vation — St. Petersburg, Pekin, Lapland, California, 
etc. The result of these calculations fixed the solar 
parallax at 8.58". This was considered accurate un- 
til lately, but has now ceased to have any value. 

The next transits wiU happen, 

December 8 1874, 

" 6 1882. 

June 7 2004. 

The first transit ever seen was witnessed by Hor- 
rex, a young amateur astronomer residing near Liv- 
erpool. His calculations fixed upon Sunday, Nov. 
24, 1639 (O. S.) 

He however commenced his watch of the sun on 
Saturday preceding. On the following day he re- 
sumed his observation at sunrise. The hour for 
church arriving, he repaired to, service as usual. Re- 
turning to his labor immediately afterward, he says : 
" At this time an opening in the clouds, which ren- 
dered the sun distinctly visible, seemed as if Divine 
Providence encouraged my aspirations ; when — oh 



CELESTIAL MEASUREMENTS. 307 

most gratifying spectacle ! the object of so many 
earnest wishes — I perceived a new spot of perfectly 
round form that had just entered upon the left limb 
of the sun." 

TIlc transits of Mercury are more frequent ; but 
owing to the nearness of the planet to the sun, 
they are of little value in determining the solar 
parallax. 

The difficulty of determining the solar parallax accu- 
rately will be seen, when one is told that the correc- 
tion from the old value of 8.58" to the new one of 
8.94", is a change in the angle equal to that which 
the breadth of a human hair would make when seen 
at a distance of 125 feet. Yet this reduces the esti- 
mated distance of the sun from 95,293,000 miles, to 
91,430,000 miles. 

4. To FIND THE LONaiTUDE OF A PLACE. — (1.) The 

solar method. — If the sailor can see the sun, he 
watches it closely with his sextant; and when it 
ceases to rise any higher in the heavens it is appa- 
rent noon. By adding or subtracting the equation 
of time (as given in his almanac), he obtains the true 
or mean noon. He then compares the local time thus 
obtained, with the Greenwich time as kept by the 
ship's chronometer. The difference in time reduced 
to degrees, etc., gives the longitude. 

(2.) The lunar method. — On account of the difficulty 
in obtaining a watch which will keep the exact 
Greenwich time through a long voyage, the moon is 
more generally relied upon than the chronometer. 



308 THE SICEKEAL SYSTEM. 

' The Nautical Almanac"^ is always published, for the 
benefit of sailors, three years in advance. It gives 
the distance of the moon from the principal fixed 
stars which lie along its path, at every hour in the 
night. The sailor has only to determine with his 
sextant the moon's distance from any fixed star, and 
then by referring to his almanac find the correspond- 
iQg Greenwich time. By comparing this with the 
local time, and reducing the difference to degrees, 
etc., he obtains the longitude. 

5. To FIND THE LATITUDE OF A PLACE. — (1.) By 

means of the sextant find the elevation of the pole 
above the horizon, and this gives the latitude di- 
rectly. (2.) In the same manner, determine the 
height of the sun above the horizon at noon. The 
sun's declination for that day (as laid down in the 
almanac), added to or subtracted from this gives the 
height of the equinoctial above the horizon. Sub- 
tract this from 90°, and the remainder is the lati- 
tude. 

* It is pleasant to notice that the astronomer can predict with 
the utmost precision. He announces that on such a year, month, 
day, hour, and second, a celestial body will occupy a certain posi- 
tion in the heavens. At the time indicated we point our telescope 
to the place, and at the instant, true beyond the accuracy of any 
timepiece, the orb sweeps into view ! A prediction of the Nauti- 
cal xilmanac is received with as much confidence as if it were a 
fact contained in a book of history. " On the trackless ocean, 
this book is the mariner's trusted friend and counsellor ; daily and 
nightly its revelations bring safety to ships in all parts of the 
world. It is something more than a mere book. It is an ever- 
present manifestation of the order and harmony of the universe." 



CELESTIAL MEASUEEMENTS. 309 

6. To FIND THE CIRCUMEERENCE OF THE EARTH. — If 

the earth were a perfect sphere, it is obvious that 
degrees of latitude would be of the same length wher- 
ever measured on its surface. Each would be -^ 
of the entire circumference. If, however, a person 
sets out from the equator, and travels along a me- 
ridian toward either pole, and when the polar star 
has risen in the heavens one degree above the ho- 
rizon, he marks the spot, and then continues his 
journey, marking each degree in succession, he will 
find that the degrees are not of equal length, but 
increase gradually from the equator to the pole. If 
now the length of a degree be measured at different 
places, the rate of variation can be found, and then 
the average length be estimated. Measurements for 
this purpose have been made in Peru, Pennsylvania 
(by Mason and Dixon), Lapland, England, France, 
India, Russia, etc. So great accuracy has been at- 
tained, that Airy and Bissel, who have solved the 
problem independently, differ in their estimate of 
the equatorial diameter but 77 yards, or only yH^ 
of a mile. 

7. To FIND THE RELATIVE SIZE OF THE PLANETS. — 

The volumes of two globes are proportional to the 
cubes of their like dimensions. The diameter of Mer- 
cury is 2,962 miles, and that of the earth 7,925 ; then. 

The volume of Mercury : the volume of the earth : : 29623 : 7925'. 

The same principle apphed to the volume or bulk 
of the sun gives — 

The bulk of the sun : bulk of earth : : 8525849 : 7925S. 



310 THE SIDEREAL SYSTEM. 

8. To FIND THE DIAMETER OF THE SUN. — (1.) A very 

simple method is to hold up a circular piece of paper 
before the eye at such a distance as to exactly hide 
the entire disk of the sun. Then we have the pro- 
portion, 

As dist. of paper disk : dist. of sun's disk : : diam. of paper d. : diam. sun's d. 

(2.) The apparent diameter of the sun, as seen 
from the earth, is about 32' : the apparent diameter 
of the earth, as seen from the sun, is twice the solar 
parallax, or 17.88". Thence, the 

Ap. diam. of earth. : ap. diam. of sun : : real diam. of earth : real diam. of sun. 

(3.) EJaowing the apparent diameter of the sun, 
and its distance from the earth, the real diameter is 
found by Trigonometry. In figure 95, let S repre- 
sent the earth, AB the radius of the sun, and ASB 
half the apparent diameter of the sun. We shall 
then have the proportion, 

AS : AB : : radius : sin. 16' (half mean diam. of sun). 

By a similar method the diameters of the planets 
are obtained. 



APPENDIX. 



TABLE ILLUSTRATING KEPLER'S THIRD LAW. (CHAMBERS.) 

In the first column are the relative distances of 
the planets from the sun ; in the second, the periodic 
times of the planets ; and in the third, the squares 
of the periodic times divided by the cubes of the 
mean distances. The decimal points are omitted in 
the third column for convenience of comparison. 
The want of exact uniformity is doubtless due to 
errors in the observations. 



Vulcan ? 
Mercury. 
Venus. . . 
Earth . . . 

Mars 

Jupiter. . 
Saturn... 
Uranus. . 
Neptune. 



.143 
.38710 
.72333 
1. 

1.52369 
5.20277 
9.53878 
19.18239 
30.03680 



19.7 

87.969 

224.701 

365.256 

686.979 

4,332.585 

10,759.220 

30,686.821 

60,126.710 



132716 
133 421 
133 413 
133 408 
133 410 
133 294 
133401 
133 422 
133405 



Arago, speaking of Kepler's Laws, says: "These interesting laws, tested 
for every planet, have been found so perfectly exact, that we do not hesitate 
to infer the distances of the planets from the sun from the duration of their 
sidereal periods ; and it is obvious that this method possesses considerable 
advantages in point of exactness." 



Measurements of the Earth's 


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Airy. 


Bessel. 




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7899.17 

7925.64 

26.47 


7899.11 

7925.60 

26.49 




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QUESTIONS. 



These are the questions which the author has used in his 
own classes for review and examination. In the historical 
portion, he has required his pupils to write articles upon the 
character and life of the various persons named, gathering 
materials from every attainable source. He has also intro- 
duced whatever problems the class could master, taking topics 
from the article on Celestial Measurements and the various 
mathematical treatises. 

Introduction. — Define Astronomy. Is the earth a planet ? 
What is the difference in the appearance of a fixed star and 
a planet? What is the Milky Way? — HISTORY. What can 
you say of the antiquity of astronomy ? How far back do 
the Chinese records extend ? Name some astronomical phe- 
nomena they contain. 

17. Why should the Chaldeans have become versed in this 
study ? How ancient are their records ? What discoveries 
did they make ? What Grecian philosopher early acquired a 
reputation in this science ? What other discovery did Thales 
make (Phil., p. 261)? What did he teach? What memora- 
ble eclipse did he predict ? What were the names of two of 
his pupils ? What did Anaximander teach ? 

18. Anaxagoras? What was his fate? In what century 
did Pythagoras live ? What was his characteristic trait ? Did 
he have any proof of his system ? Explain his theory. How 
does it differ from ours ? What strange views did he hold ? 
What theory did Eudoxus advance ? 

19. What is the theory of the crystalline spheres ? What 
has Hipparchus been styled? What addition did he make 
to astronomical knowledge? How many stars in our present 
catalogue (p. 228) ? How did Egypt rank in science at an 
early day? What preparation did the Grecian philosophers 
make to fit themselves for teachers ? How long did Pythag- 
oras travel for this purpose ? What can you say of the school 
at Alexandria? What great work did Ptolemy write there? 
What theory did he expound ? 



316 QUESTIONS IN ASTRONOMY. 

20. Was it original ? What discovery did Eratosthenes 
make? Describe that method (p. 309). Show how the 
movements of the planets puzzled the ancients. What was 
the theory of " cycles and epicycles?" 

21. Did the ancients believe in the reality of this cumbrous 
machinery? Did this theory possess any accuracy? Could 
they adapt it to explain any new motion ? 

22. What was the remark of Alphonso ? When did astron- 
omy cease to be cultivated as a science ? In what century ? 
Why did Caesar import an astronomer ? Why did he attempt 
to revise the Calendar? What change did he make (p. 295)? 
State something of the repute in which astrology was held. 

23. Tell what you can of the system. What use did it sub- 
serve ? What theory displaced the Ptolemaic ? When ? 
Was the system of Copernicus original ? What credit is due 
him ? Describe his idea of apparent motion. How did he 
apply this to the heavenly bodies ? 

24. What crudity did he retain ? Who was Tycho Brahe ? 
What was his theory? How did it differ from Ptolemy's and 
Copernicus's ? 

25. What good did he accomplish? Could he generalize 
his facts ? Had he a telescope ? How did Kepler differ from 
Brahe ? What were the two prominent characteristics of Kep- 
ler ? Give his three laws. Tell how he discovered the first. 
The second. The third (p. 313). Describe the ellipse. De- 
fine focus, perihelion, and aphelion. What remarkable state- 
ment did Kepler make ? 

29. When did Galileo live ? What discoveries did he make 
in Natural Philosophy? In Astronomy? What advantage 
did he have over his predecessors ? 

30. Give an account of his observations on the moon. On 
Jupiter's moons. 

31. Why did this settle the controversy between the Ptole- 
maic and the Copernican system? How were Galileo's dis- 
coveries received ? Give some of Sizzi's ponderous arguments. 

33. Who discovered the law of gravitation ? Repeat it. 
How was this idea suggested ? What familiar laws of motion 
aided Newton ? How did he apply these to the motion of the 
moon ? Repeat the story of his patient triumph. 

35. What is the celestial sphere ? Give the two illustrations 
which show its vast distance from the earth. 

36. Why can we not see the stars by day, as by night ? 
What portion of the sphere is visible to us ? Name the three 
systems of circles. 

37-41. Name and define (i) the principal circle, (2) the 



QUESTIONS IN ASTEONOMY. 317 

secondary circles, (3) the points, and (4) the measurements 
of each system. Define, especially, because in common use, 
zenith, nadir, azimuth, altitude, equinoctial, right ascension, 
declination, equinox, ecliptic, colure, and solstice. What is N 
or S in the heavens ? What is the Zodiac ? 

42. How wide ? How ancient ? How divided ? Give the 
names and signs. State the meaning of each (p. 229). 

n. The Solar System. 

Of what is the solar system composed ? Describe how we 
are to picture it to ourselves. 

The Sun. — Its sign. Its distance from us? Illustrate. 

47. How are celestial distances measured ? To what is the 
sun's light equal ? To how many full moons? Its heat ? Illus- 
trate. What proportion of the sun's heat reaches the earth ? 

48-50. Its apparent size ? How does this vary ? Its dimen- 
sions — (i) diameter — illustrate, (2) volume, (3) mass, (4) 
weight, (5) density. How large did Pythagoras think the sun 
is ? Tell something about the force of gravity in the sun. 
How much would you weigh if carried to its surface ? (This 
can be calculated from the table in Appendix. ) How does the 
sun appear to the naked eye ? How can we see the spots ? 
What were formerly the views of astronomers with regard to 
the sun's face ? When were the spots discovered ? 

52. Tell something about the number of the spots. Their 
location. Size. 

53. Describe the parts of which they are composed. The 
motion of the spots. 

54-5. How do they change in form as they pass across the 
disk ? What does this prove ? What is the length of a solar 
axial revolution ? Explain a sidereal and a synodic revolution. 

56-7. Why do not the spots move in straight lines? Show 
how they curve. Tell what you can about the irregular move- 
ments of the spots. Tell how suddenly they change. 

58. What can you say about their periodicity? Who dis- 
covered this ? Is there any connection between the solar spots 
and the aurora? Tell the influence of the planets on the spots. 
Explain, 

59. Do the spots affect the fruitfulness of the season ? Does 
the temperature of the spots differ from that of the rest of the 
sun ? Are they depressions in the sun ? How much darker 
are they than the adjacent surface ? 

60. Is the sun brighter than the Drummond light? Afis. 
The sun gives out as much light as one hundred and forty-six 



318 QUESTIONS IN ASTKONOMY. 

lime-lights would do, if each were as large as the sun and 
were burning all over. What are the faculae ? Describe the 
mottled appearance of the sun. 

6i. What is the shape of the bright masses? What is a 
pore? 

62. Describe the constitution of the sun according to Wil- 
son's theory. How are the spots produced ? The faculas ? 

63. The penumbra ? The umbra? 

64. What is Kirchhoff's theory? How are the spots pro- 
duced? The umbra? The penumbra? Upon what does 
this theory depend (p. 286) ? What is the cause of the 
heat of the sun ? Will the heat ever cease ? * 

The Planets. — Name the six characteristics common to 
all the planets. 

(>']. Compare the two groups of the major planets. 

68. Draw an ellipse, and name the various parts. Define 
the ecliptic, f The ascending node. The descending node. 
Line of the nodes. Longitude of the node. Tell what you 
can with regard to the comparative size of the planets. 

71. What is a conjunction ? Name the earliest that are re- 
corded. 

72. Tell what you can concerning the planets being in- 
habited. 

74. What about the conditions of life on the diiTerent 
planets ? What are the two divisions of the planets ? 

75. What causes the apparently irregular movements ot 
the planets ? Define heliocentric and geocentric place. Il- 
lustrate. In what part of the sky is an inferior planet always 
seen ? Define inferior and superior conjunction. 

76. Greatest elongation. Quadrature. Why is a star at 
one time "evening" and at another "morning star?" 

^']. What is a transit ? Explain the retrograde motion of 
an inferior planet. (This motion, it will be remembered, was 
one that sorely puzzled the ancients. ) 

*If we accept the Nebular hypothesis (p. 283), we must suppose that 
the heat is produced by the condensation of the nebulous matter and con- 
sequent chemical changes. The sun is radiating its heat constantly, and, 
after a time, will go out, in turn, as the earth and all the planets have be- 
fore it. 

■j-Lockyer beautifully says : "We may imagine the earth floating around 
the sun on a boundless ocean, both sun and earth being half immersed in it. 
This level, this plane, the plane of the ecliptic (because all eclipses occur 
in it), is used by astronomers as we use the sea-level. We say a moun- 
tain is so far above the level of the sea. The astronomer says a star is so 
high above the level of the ecliptic." 



QUESTIONS IN ASTEONOMY. 319 

yS. Describe the phases of an inferior planet. Why does 
an inferior planet have phases ? Define gibbous. 

79. Explain the opposition and conjunction of a superior 
planet. Its retrograde motion. Must a superior planet al- 
ways be seen in the same part of the sky as the sun ? 

80. Which retrogrades more, a near or a distant planet ? 
Define a sidereal and a synodic revolution of an inferior and a 
superior planet, and tell what you can about each. In what 
case would there be no difference between a sidereal and a 
synodic revolution ? Why is a planet invisible when in con- 
junction ? 

82. When is a planet evening, and when morning star ? 
Tell what you can about the supposed discovery of a planet 
interior to Mercury. 

S;^. Mercury. — Definition and sign? Describe the appear- 
ance of Mercury, and where seen. 

84. What was the opinion of the ancients ? The astrolo- 
gists ? Chemists ? Why is it difficult to see it ? When can 
we see it best ? 

85. What is the peculiarity of its orbit? Its distance from 
the sun? Velocity? Length of its day? Year? Difference 
between its sidereal and synodic revolution ? why ? Its dis- 
tance from the earth ? 

86. Show why its greatest and least distances vary so much. 
What is its diameter ? Volume ? Density ? Force of 
gravity ? Specific gravity ? How much would you weigh on 
Mercury? Describe its seasons. (If the pupil does not un- 
derstand pretty well the subject of the terrestrial seasons, it 
would be well here to read carefully page no, et seq. ) 

88. Its temperature ? Appearance of the sun ? Has it any 
moon? What is the appearance of the planet through a 
telescope ? What do these phases prove ? What do we know 
of its mountains and valleys ? 

89. Venus. — Definition and sign? Ancient names? Ap- 
pearance to us ? 

90. When brightest ? Can Venus be seen by day ? Il- 
lustrate. 

91. Describe the orbit. What is the distance of Venus 
from the sun ? Velocity ? Length of the year ? Day ? Dif- 
ference between the sidereal and synodic revolution ? Dis- 
tance from the earth ? 

92. How does the apparent size vary ? When is Venus the 
brightest ? What is the diameter ? Volume ? Density ? 

93. Force of gravity? Does the force of gravity increase 



320 QUESTIONS IN ASTEONOMY. 

or decrease with the mass or volume of the body ? Describe 
the seasons. 

94. Describe the telescopic appearance. Who discovered 
the phases of Venus ? What was Copernicus's idea ? 

95. What proof have we of an atmosphere? Of clouds? 
Has Venus any moon ? 

96. Earth. — Sign? What is the appearance of the earth 
from the other planets? Do we, then, live on a star? Is it 
probable that the earth was always dark and dull as it now 
seems to us ? * How does the size of the earth compare with 
that of the other planets ? Form of the earth ? Exact diam- 
eter ? Is the equator a perfect circle ? 

98. Circumference ? Density ? Weight ? What can you 
say of its inequalities ? How do you prove the rotundity of 
the earth ? 

99. Why can we see further from the top of a hill than 
from its base ? Why is the horizon a circle ? 

100. Give some illustrations of apparent motion. 

loi. Explain the cause of the rising and setting of the sun 
and stars. Who first explained it in this manner ? What do 
you say of its simplicity ? 

102. Cause of day and night? Do all places on the earth 
revolve with equal velocity ? Illustrate. At what rate do we 
move? 

103. Why do we not perceive our motion ? What would 
be the effect if the earth were to stop ? 

104-5. Is there any danger of this catastrophe ? Draw the 
figure, and show how the stars move daily through unequal 
orbits and with unequal velocities. Describe the appearance 
of the stars at the N. Pole. 

106. At the Equator. S. Pole. Describe the path of the 
earth about the sun. Define eccentricity. Is this stable ? 

107. Do we see the same stars at different seasons of the 
year? Why not? If we should watch from 6 P. M. to 6 A. M., 
what portion of the sphere could we see ? What do we 
mean by the yearly motion of the sun among the stars? How 
can we see it ? 

109. What is the cause? What is the ecliptic? Why so 
called ? What are the equinoxes ? What do we understand 

* Probably not. The earth was doubtless once a glowing star, like the 
sun. Its crust is only the ashes and cinders of that fearful conflagration. 
The rocks are all burnt bodies. The atmosphere is only the gas left over 
after the fuel was all consumed. Every organic object has been rescued by 
plants and the sunbeam from the grasp of oxygen. 



QUESTIONS IN ASTRONOMY. 321 

when we see in the almanac '' the earth is in Aries ?" " The 
sun is in Sagittarius ?" 

no. How many apparent motions has the sun? Nam.e 
them, and give the cause and effects of each. Has the sun any- 
real motions (pp. 54 and 224) ? Describe the apparent mo- 
tion of the sun, N. and S. How is it that the sun in summer 
shines on the north side of some houses both at rising and 
setting, but in winter never does ? Define the obliquity of the 
ecliptic. The parallelism of the earth's axis. What do you 
say of its permanence ? 

112. Why will a top stand while spinning, but will fall as soon 
as it ceases ? Show how the rays of the sun strike the various 
parts of the earth at different angles at the same time. Show 
how the angles vary at different times. Is the sun really hotter 
in summer than in winter? Why does it seem to be ? 

113. Explain the cause of equal day and night at the 
Equinoxes. Why are our days and nights of unequal length 
at all other times ? Why do they vary at different seasons of 
the year? How do the seasons, &c,, in the N. Temperate 
Zone compare with those in the S. Temperate Zone ? De- 
scribe the yearly path of the earth about the sun — (i) at the 
summer solstice ; (2) at the autumnal equinox; (3) at the 
winter solstice ; (4) at the vernal equinox ; (5) the yearly path 
finished back to the starting-point. Is the division of the 
earth's surface into zones an artificial or a natural distinction ? 
Who invented it ? 

117. How much nearer are we to the sun in the winter? 
Why is it not the warmest at that time ? How is it in the 
South Te :-»perate Zone ? When do the extremes of heat and 
cold occur ? Why not exactly at the solstices ? 

118. Why is summer longer than winter? Does the earth 
move with the same velocity in all parts of its orbit ? Describe 
the curious appearance of the sun at the North Pole. In 
Greenland, at what part of the year will the midnight sun be 
seen due north ? What is the length of the days and nights 
at the Equator ? 

119. Describe the results if the axis of the earth were per- 
pendicular to the ecliptic. 

120. If the equator were perpendicular to the ecliptic. De- 
fine precession of the equinoxes. Who discovered this? At 
what rate does this movement proceed ? What is the amount 
at present ? 

121. What are the results? What star was formerly the 
Pole star ? 

123. Explain the cause of precession. 



322 QUESTIONS IN ASTBONOMY. 

125. How does the spinning of a top illustrate this subject? 

126. What is Nutation? Cause? How does the moon's 
influence compare with that of the sun ? 

127. What is the real path of the N. Pole through the 
heavens ? Is the obliquity of the ecliptic invariable ? What 
is the limit ? What is the effect of this variation ? 

128. Are the solstices and equinoxes stationary? What is 
the result of this change on the seasons ? When will the 
cycle be completed ? When is the sun in perigee ? 

129. What do you say of the provisions made to secure 
permanence, so that slight changes themselves prevent greater 
changes ? 

130. What is refraction? Its effect? 

131. How does it vary? 

132. Are the sun and moon ever where they seem to be? 
Is the real day longer or shorter than the apparent one ? 
Why do the sun and moon appear flattened when near the 
horizon ? Why not when they are high in the heavens ? 
Why do they appear smaller in the latter case ? 

133- What causes the hazy appearance of the heavenly 
bodies near the horizon ? What is the cause of twilight ? 
How long does it last ? Is it the same at all seasons of the 
year ? 

134. At all parts of the earth? Where is it longest? 
Shortest ? What is diffused light ? What would be the effect 
if the atmosphere did not act in this way ? Is there really any 
sky in the heavens ? Cause of the appearance ? 

135. What is aberration of light? Illustrate. Give two 
reasons why we never see the sun where it really is. 

137. The general effect of aberration ? Define parallax. 
Illustrate. 

138. Define true and apparent place. How does parallax 
vary ? What is the practical importance of this subject (p. 
300, et seq. ) ? 

139. Define horizontal parallax. What is the sun's hori- 
zontal parallax ? What is the annual parallax ? 

The Moon. — Signs ? Describe its orbit. 

140. Its distance from the earth ? Illustrate. Difference 
between its sidereal and synodic revolution? 

141. What is the real path of the moon? (Imagine a pen- 
cil fastened to the spoke of a wheel, and the wheel rolled by 
the side of a wall on which the pencil is constantly marking. ) 
How often does it turn on its axis ? What is the moon's di- 
ameter ? Volume ? How does its apparent size vary ? Why 
does it api->ear larger than it really is ? 



QUESTIONS IN ASTRONOMY. 323 

142. Why does the crescent moon appear larger than the 
dark body of the moon ? When ought the moon to appear 
the largest? Do all persons think the moon of the same ap- 
parent size ? Explain the three librations of the moon. 
- 143. How does moonhght compare with sunlight? Is there 
any heat in moonlight ? Why is it generally clear at full 
moon ? Does the centre of gravity in the moon coincide with 
that of magnitude ? Has the moon any atmosphere ? What 
proof have we of this? — Afts. (i) We see but slightly if any 
appearance of twilight in the moon. (2) When the moon 
passes between us and a star, it does not refract the light of 
the star, so that the atmosphere cannot be sufficient to sup- 
port more than too of an inch of the mercurial column. 

144. How does the earth appear from the moon ? What is 
the earth-shine ? How is it caused ? What is it called in 
England ? Describe the path of the moon around the earthy 
and the consequent phases. Why is new moon seen in the 
west and full moon in the east ? Why can we sometimes see 
the moon in the west after the sun rises, and in the east before 
the sun sets ? 

147. Length of a lunar month ? What do we mean by the 
moon's running high or low? Cause? Use? 

148. What is harvest moon? Hunter's moon? Cause? 

149. What are nodes ? How much is the moon's orbit in- 
clined to the ecliptic — our ideal sea-level ? What is an oc- 
cultation ? Use ? 

150. Describe the seasons, heat, &c., on the moon. 

152. Telescopic appearance of the moon ? Are the mount- 
ains the light or dark portions ? What can you say about 
them ? The gray plains ? The rills ? The craters ? What 
are the peculiar features, then, of the lunar landscapes ? Are 
the lunar volcanoes extinct ? 

Eclipses, — When can an eclipse of the sun occur? Show 
how a solar eclipse may be total, partial, or annular. 

156. Define umbra. Penumbra. Central eclipse. State 
the general principles of a solar eclipse. 

158. What curious phenomena attend a total eclipse? 

159. Describe the effect of a total eclipse? 

160. What curious custom prevails among the Hindoos? 
What is the Saros ? Cause ? 

161. Is it now of any value? What is the metonic cycle? 
Explain its use. 

162. What is the golden number? Cause of a lunar 
eclipse ? Draw the figure and describe it. Why are lunar 
eclipses seen oftener than solar ones ? 



324 QUESTIONS IN ASTEONOMY. 

163. What is the earhest account of an ecHpse? How were 
eclipses formerly regarded ? 
' 164. What story is told of Columbus ? 
The Tides.* — Define ebb. Flow. How often does the 
tide happen ? Explain the cause. 

166. Why does the tide occur fifty minutes later each 
day ? Why is there a tide on the side opposite the moon ? 
The sun is much larger than the moon ; why does it not pro- 
duce the larger tide ? Why is not the tide felt out at sea ? 

167. What is spring-tide? Neap-tide? Causes? Why 
does the tide differ so much in various localities ? Tell about 
the height of the tide at different points. 

168. Why is there no tide on a lake ? 
Mars. — Definition and sign? 

169. Describe its appearance. When is it brightest ? Its 
distance from the sun ? Velocity ? Day ? Year ? 

170. Distance from the earth? Peculiarity of its orbit? 
Diameter? Volume? Density? Mass? Force of gravity? 
Figure ? Describe its seasons. 

171. Has it any atmosphere? Moon? Appearance of 
our earth? Telescopic features. (The land and sea features 
have been so well decided that they have been named, and a 
Mars's globe made.) 

172. Cause of its ruddy color? What are the snow-zones? 
Can we watch the change of its seasons ? 

Minor Planets (Asteroids). — Give Bode's law. Tell 
how the first of these planets was discovered. How many are 
now known? — A7is. There are (Aug. 1870) 109. Are they 
probably all discovered ? 

174. Describe these " pocket planets." Are they all found 
within the Zodiac? What is their origin? — Ans. According 
to the Nebular hypothesis, the ring of matter broke up into 
numberless small bodies instead of aggregating into one large 
planet. Give some of the names and signs. 

Jupiter. — Definition and sign? Describe its appearance. 
Ancient views. Describe its orbit. What is its distance from 
the sun? Velocity? (1869. 2; is in t). Day? Year? Dis- 
tance from the earth ? 

177. Diameter? Volume? Density? Centrifugal force? 

* As the tidal wave does not move as rapidly as the earth does, the 
water has an apparent backward motion. It has been suggested that this 
acts as a break on the earth's diurnal revolution. It has been shown that 
the moon's true place can be best calculated if we suppose that the sidereal 
day is shortening, by tidal action, at the rate of -^g of a second in 2,500 
years. 



QUESTIONS IN ASTEONOMY. 325 

Force of gravity ? Figure ? Describe its seasons. Upon what 
does the change of seasons in any planet depend? 

178. The appearance of the sky ? The telescopic features ? 
Are Jupiter's moons visible to the naked eye? 

179. How named? What is their size? What space do 
they occupy? 

180. Describe the eclipse of the moons. 

181. Define immersion, emersion, and transit. How rapid- 
ly do the satellites revolve ? What can you say of the fre- 
quency of eclipses on Jupiter ? Describe the belts. Why are 
they parallel to its equator ? 

182. How was the velocity of light discovered ? 
Saturn. — Definition and sign? Describe its appearance. 

How rapidly does it move through the sky? (1869. v is in m). 
Its distance from the sun ? Pecuharity of its orbit ? 

184. Velocity? Year? Day? Distance from the earth? 
Diameter ? Volume ? Density ? Force of gravity ? De- 
scribe its seasons. 

185. Has it any atmosphere? Who discovered the rings 
of Saturn ? Describe them. 

186. Are they stationary? Explain their phases. 

187. Describe Saturn's belts. 

188. Describe Saturn's moons. The scenery on Saturn. 
Uranus. — Definition and sign ? How was it discovered? 

Tell of its previous discovery by Le Monnier. Is Uranus 
visible to the naked eye ? (1869. lit is in ©). Distance from 
the sun? Year? Diameter? Density? 

191. Describe its seasons. Telescopic features. Satellites? 
Peculiarity of its moons. 

Neptune. — Definition and sign ? Appearance in the sky? 
Give an account of its wonderful discovery. 

193. What is its distance from the sun ? Year ? Velocity ? 
Diameter? Volume? Density? Do we know anything of 
the seasons ? Why not ? Intensity of the light ? 

194. Appearance of the heavens? What are the telescopic 
features ? Has Neptune any moon ? What advantage have 
the Neptunian astronomers ? 

Meteors, Aerolites, and Shooting-Stars. — Define an 
aerolite. A shooting-star. A meteor. Give some account 
of the fall of meteors (aerolites). 

197. What elements are found in aerolites ? How can an 
aerolite be distinguished ? Give an account of wonderful 
meteors. 

198. Of shooting-stars. 

199. Describe the showers of 1799 and 1833. 



326 QUESTIONS IN ASTRONOMY. 

200. The shower of 1866. At what inten-als did these 
showers occur? Why was not the shower of 1866 seen in this 
country ? Ans. It came in the daytime. 

201. What is the average number of meteors and shooting- 
stars daily ? Why do we not see more of them ? 

202. In what months are they most abundant? Describe 
the origin of meteors and shooting-stars. What is their 
velocity? W^hat causes the light? The explosion often 
heard ? What is said of a companion to our moon ? 

203. What is the theory of meteoric rings? What is their 
shape ? How do these account for the showers at regular in 
tervals ? 

204. What is the period of the November ring ? Why is 
the August shower so uniform, while the November one is only 
periodic ? 

205. What is the relation between meteors and comets? 
What do you mean by the radiant point ? What effect do 
meteors have on the weather ? 

206. What is their height ? \Veight ? 

Comets. — How were they looked upon by the ancients ? Il- 
lustrate. Define the term comet. What is the tail ? The 
nucleus? The head ? Thecoma? Does each comet neces- 
sarily possess all these parts ? How would a mere round, 
fleecy mass be known to be a comet ? What mistake did 
Herschel make in looking, as he supposed, at one of this 
kind (p. 189)? 

208. Where do comets appear? In what direction do they 
move ? How does a comet look when first seen ? Upon what 
does the time of greatest brilliancy depend ? What do you say 
of the number of the comets ? What was Kepler's remark ? 

209. Why do we not see them oftener ? Where did Seneca 
see one ? Describe the orbits of comets. Which class has 
been calculated ? Which classes never return ? 

210. Describe the difficulty of calculating a comet's orbit. 

211. Name the periods of some. What has been the dis- 
tance from the sun of some noted comets ? Velocity ? 

212. What do you say of the density of a comet ? Illustrate. 
Is there any danger of our running against a comet ? 

213. Do comets shine by their own or by reflected light? 
Tell what you can of their variation in form and dimensions. 

214. Give some account of the comets of 181 1, 1835, and 
1843. For what is Encke's comet noted ? What is its period? 
Give some description of Donati's comet. 

Zodiacal Light. — Where can this be seen? What is its 
appearance ? Where is it brightest ? What is its origin ? 



QUESTIONS IN ASTRONOMY. 327 



III. — The Sidereal System. 

Tell something of the appearance of the heavens at Nep- 
tune's distance from the sun — our starting-point? Do we 
ever see the stars ? What do we see, then ? 

222. Which star is nearest the earth ? What is its paral- 
lax? Its distance ? What is Prof. Airy 's remark ? 

223. How long would it take light to reach the nearest star ? 
How would the earth's orbit appear at that distance ? Our 
sun ? How long does it take for the light of the smaller stars 
to reach the earth ? What can you say of the motion of the 
fixed stars? Illustrate. 

224. What proof have we that the stars are suns ? (''If 
Sirius shines as brightly as our sun, at its distance, it must be 
three thousand times larger." — LOCKYER.) That our sun is 
only a small star ? Describe the motion of the solar system. 
What is the centre ? How many stars can we see with the 
naked eye ? With a telescope ? Have all the stars been dis- 
covered ? 

226. What is the cause of the twinkling of the stars ? Do 
the stars twinkle in tropical regions ? Why not ? What do 
you say of the magnitude of the stars? Name four points 
of difference between a planet and a fixed star. 

227. What do you mean by a star of the first magnitude ? 
How many are there? Of the second magnitude? How 
many sizes may one see with the naked eye ? With a tele- 
scope ? What is the cause of the difference in the brightness 
of the stars ? What can you say of the names of the stars ? 

228. What can you say with regard to the division of the 
stars into constellations ? Is there any real likeness to the 
mythological figures ? Name any figure which seems to you 
well founded. 

229. Are the boundaries distinct ? Who invented the sys- 
tem ? Give the meaning of the signs of the Zodiac and their 
origin. 

230. Explain why the signs and constellations of the Zodiac 
do not agree. 

231. What causes the appearance of the constellations? 
Would they appear as they now do, if we should go out into 
space among them ? 

232. Are the present forms permanent ? State the value of 
the stars in practical life. 

233. What were the views of the ancients with regard to 
the stars? 



328 QUESTIONS IN ASTKONOMY. 

234. Describe the division of the stars into three zones, and 
name them. 

The Constellations. — The questions on these are uni- 
formly : (i) description, {i) principal stars, and (3) mythologi- 
cal history. They need not therefore be repeated with each 
constellation. — What are the pointers? Does Polaris mark 
the exact position of the North Pole ? How many times per 
day is Polaris on the meridian of any place ? Explain how 
this applies in navigation or surveying. State how the amount 
of the variation from the true north will change through the 
ages. What star will ultimately become the pole-star ? What 
curious facts are stated concerning the Pyramids ? What do 
you say of the distance of Polaris ? How may latitude be 
calculated by means of Polaris ? 

Double Stars, etc. — Does any star appear double to the 
naked eye ? How many have been found by the use of the 
telescope ? What is an optical double star ? Are all double 
stars of this class ? Describe the revolution of a binary sys- 
tem. What other combinations have been discovered ? Their 
periods ? 

266. Orbits ? Mass ? Are these companion stars as close 
to each other as they seem ? What can you say of the colored 
stars ? Do their colors ever change ? Which colors would in- 
dicate the hottest star ? 

267. What is the probable effect in a system having colored 
suns ? What are variable stars ? Describe the changes of 
Algol. 

268. Of Mira. What is the cause ? What are temporary 
stars ? Describe the one seen in Cassiopeia. 

269. The one in Corona Borealis, in 1866. What are lost 
stars ? 

270. Can you give any explanation ? Of what did the star 
of 1866 consist? Are these stars destroyed? Is the process of 
creation now complete ? 

271. What are star clusters ? Name several. 

272. Is such a grouping a mere optical effect? Are they 
probably as closely compacted as they seem to be ? What 
are nebulae ? How do they differ from clusters ? Is it proba- 
ble that all nebulce will be resolved into clusters ? What has 
^spectrum analysis proved some of the nebulas to be ? 

273. Are they suns? Where are they most abundant? 
What can you say about their distances ? Into how many 
classes are they divided ? Describe and illustrate the elliptic 
nebula:-. What is said of the distance of the great nebula in 
Andromeda ? The number of stars it contains ? Describe 



QUESTIONS IN ASTRONOMY. 329 

the annular nebulcC. What is said of the ''ring universe" 
in Lyra ? 

276. Its diameter? Describe the spiral nebula in Canes 
Venatici. Describe the planetary nebulae. What is said of 
the number and size of these "island universes?" 

277. Describe the fantastic appearance of the irregular 
nebula. What are nebulous stars ? What is the cause ? 

278. What is said of the size of the one in Cygnus ? What 
are variable nebulae ? 

279. Give instances. What is said of double nebulae ? Is 
anything definite known with regard to them? What are the 
Magellanic clouds ? 

280. Describe the Milky-way. What can you say of the 
number of stars in the Galaxy? Are the stars uniformly dis- 
tributed ? 

281. What is Herschel's theory of the constitution of the 
universe ? If this theory be true, what is our sun ? 

282. Give an account of the Nebular hypothesis. What is 
said of Saturn's rings ? May they ultimately disappear ? 

284. What is spectrum analysis? Name the three kinds of 
spectra. 

285. What colored rays will a flame absorb ? Describe the 
spectroscope. 

286. What are Fraunhofer's lines ? What is known of the 
constitution of the sun ? What proof have we that iron exists 
in the sun ? 

287. What elements have been found in the sun ? What 
proof have we that the stars are suns ? What can you say of 
the similarity existing between the stars and our earth ? 

288. What has been discovered with regard to the constitu- 
tion of the Nebulae ? Of their relative brightness ? 

Time. — What two methods of measuring time ? What is a 
sidereal day ? 

289. What are astronomical clocks ? Tell how they are 
used. Why do astronomers use sidereal time ? What is a 
solar day? What causes the difference between a sidereal and 
a solar day ? To how much time is a degree of space equal ? 

290. Which is taken as the unit, the solar or the sidereal 
day ? How long is a solar day ? A sidereal day ? A solar 
day equals how many sidereal hours? A sidereal day equals 
how many solar hours ? Describe mean solar time. What is 
apparent noon ? Mean noon ? The equation of time ? When 
is this greatest ? When least ? 

291. When do mean and apparent time coincide? Can a 
watch keep apparent time ? How may apparent time be kept? 



330 QUESTIONS IN ASTRONOMY. 

How can it be changed into mean time ? Tell how to erect a 
sun-dial. When will a sidereal and a mean-time clock co- 
incide ? A mean-time clock and the sun-dial? 

292. Give the two reasons why the solar days are of unequal 
length. 

294. What is the civil day ? Who invented the present 
division ? Describe the customs of various nations. What 
is the origin of the names of the days ?* What is the sidereal 
year ? The mean solar year ? What causes the difference ? 

295. What is the anomalistic year ? How did the ancients 
find the length of the year ? What error did they make ? 
What was the result ? Give an account of the Julian calendar. 
The Gregorian calendar. What is the meaning of the terms 
O. S. and N. S. ? What country now uses O. S. ? When 
was the change adopted in England ? How was it received ? 
How could a child be eight years old before a return of its 
birthday ? 

297. When do the Jews begin their year ? Why does our 
year begin January ist ? Show how the earth is our timepiece. 
What influence has Jupiter's moons on the cotton trade ? 

Celestial Measurements. — These problems are to be 
used throughout the study. They require no questions but 
the formal statement of the problem requiring solution. 



* It is said that the Egyptians named the seven days from the seven 
celestial bodies then known. The order vi^as continued by the Romans. 
Tuesday they called Dies Martis ; Wednesday, Dies Mercurii • Thursday, 
Dies yo-vis ,• Friday, Dies Veneris. In the Saxon mythology, Tius, Wo- 
den, Thor, and Friga are equivalent to Mars, Mercury, Jupiter, and 
Venus. Hence we see the origin of our English names. 



GUIDE TO THE CONSTELLATIONS. 



The following is a description of the appearance of the heavens on or about 
the first day of each month in the year. 

January. (7 p. m.) — In the North, Cassiopeia and Per- 
seus are above Polaris, Cepheus and Draco west, Ursa Minor 
below, and Ursa Major below and to the east. In the East, 
Cancer is just rising, Canis Minor (Procyon) has just risen. 
Alojig the Ecliptic, Gemini is well up, then Taurus, Aries 
reaches to the meridian, next Pisces, Aquarius (letter Y) and 
Capricornus just setting. In the Southeast, Orion and the 
Hare are well up. In the South, Cetus swims his huge bulk 
far to the east and west. In the Southwest is Piscis Australis 
(Fomalhaut). North of the Ecliptic the Triangles are nearly 
in the zenith, Perseus is just east, below is Auriga, Androme- 
da lies just west of the meridian, and Pegasus is midway, while 
Delphinus (the Dolphin, Job's Coffin), Aquila (Altair), and 
Lyra (Vega) are fast sinking to the western horizon. 

February. (7 p. m.) — In the North, Ursa Major lies 
east of Polaris, Ursa Minor and Draco below, Cepheus west, 
Cassiopeia above and to the west. In the East, Regulus and 
Cor Hydrae are just rising. Along the Ecliptic, Leo (Regulus, 
the sickle) just rising. Cancer well up, Gemini midway, Taurus 
on the meridian, Aries (the scalene triangle) past, Pisces 
next, and lastly Aquarius just setting. In the Southeast, 
Canis Minor, Canis Major (Sirius), and Orion are conspicuous. 
In the Southwest, Cetus covers nearly the whole sky. North 
of the Ecliptic, Perseus is on the meridian, while Auriga is a 
little east of it ; west of Perseus is Andromeda, while the great 
square of Pegasus is fast approaching the horizon. 

March. (7 p. M.)—In the North, Ursa Major lies east 
of Polaris, Draco and Ursa Minor below, Cepheus below and 
to the west, and Cassiopeia west. In the East, Cor Caroli 
(the Greyhound) is well up, and Coma Berenices is rising. 
Alo7ig the Ecliptic, Leo is fully risen, next Cancer, Gemini 
reaches to the meridian, Taurus is past, Aries midway, and 
lastly Pisces is just beginning to set. In the Southeast. Cor 



332 GUIDE TO THE CONSTELLATIONS. 

Hydrae, Canis Minor and Canis Major are conspicuous. In tin 
South, Orion blazes brilliantly. In the Southiuest, Cetus is 
hiding below the horizon. North of the Ecliptic, Auriga is in 
the zenith ; west are Perseus and Andromeda, while Pegasus 
is just beginning to sink out of sight. 

April. (7 p. M.) — In the North, Ursa Major is above and 
to the east of Polaris ; opposite and to the west is Perseus, 
Draco below and to the east, Cepheus below and to the west, 
Cassiopeia west. Li the East, Bootes (Arcturus) not quite fully 
risen. Along the Ecliptic, Virgo (Spica) rising, Leo midway, 
Cancer reaches to the meridian, Gemini past, next Taurus, 
then Aries, and lastly Pisces just setting. I71 the Southeast is 
the Crater (the Cup), and Hydra stretches its long neck to the 
meridian. Bt the South, Canis Minor. I71 the Southwest, 
Sirius and Orion. North of the Ecliptic, and in the northeast, 
are Coma Berenices and Cor Caroli; above Gemini and Taurus 
is Auriga, while Andromeda is just setting in the northwest. 

May. (8 p. m.) — In the North, Ursa Major is above Polaris, 
Ursa Minor and Draco east, Cepheus and Cassiopeia below, 
and Perseus west. Ei the East, Lyra is just rising, and Her- 
cules is just up. Along the Ecliptic, Libra is just rising, Virgo 
is midway, Leo is on the meridian, Cancer is past, next Gemini, 
and lastly Taurus just setting. In the Sotith, stretching east 
and west of the meridian, is Hydra, with the Crater and Cor- 
vus a little east. I?i the Soicthwest, is Cor Hydree, Canis Major, 
and Canis Minor, while Orion is just setting in the west. North 
of the Ecliptic, in the east, above Hercules, are Corona Bore- 
alis (The Northern Crown), Bootes (Arcturus), Coma Bere- 
nices, and Cor Caroli, \vhich stretch nearly to the meridian. I?i 
the Northwest, above Taurus and Perseus, is Auriga. 

June. (8 p. M.)—In the North, Ursa Major is above Po- 
laris, Draco and Ursa Minor to the east, Cepheus below and 
to the east, and Cassiopeia directly below. In the East, Cyg- 
nus and Aquila are just rising, Lyra and Taurus Poniatowskii 
are well up. Along the Ecliptic, Scorpio is rising. Libra is mid- 
way, Virgo on the meridian, Leo past. Cancer midway, 
Gemini next, and Taurus just setting. In the South are Cor- 
vus and the Crater, a little past the meridian. Ei the South- 
west is Cor Hydrse, and in the west Canis Minor approaching 
the horizon. North of the Ecliptic, in the east, above Scorpio, 
is Hercules ; then Corona and Bootes, and near the meridian. 
Cor Caroli and Coma Berenices. In the Northwest is Auriga, 
just coming to the horizon. 

July. (9 p. u.)—In the North, Draco and Ursa Minor 



GUIDE TO THE CONSTELLATIONS. 333 

above Polaris,. Ursa Major west, Cepheus east, and Cassi- 
opeia below to the east. In the East, the Dolphin (Job's 
Coffin) is now well up, Cygnus is almost midway to the me- 
ridian, and Lyra is still higher. Along the Ecliptic, Capri- 
cornus is rising, Sagittarius (the Archer) is next, Scorpio, with 
its long tail swinging along the horizon, is directly south. 
Libra is past the meridian, Virgo midway, and Leo has almost 
reached the horizon. In the Southwest, the Crater is setting, 
and Corvus is just above. North of the Ecliptic, above Scorpio 
and east of the meridian, are Serpentarius, Hercules, and 
Taurus Poniatowskii ; Corona is almost on the meridian, to 
the west of which lie Bootes, Cor Caroli, and Coma Berenices. 

August. (9 P. M.) — In the North, Draco and Ursa Minor 
are above Polaris, Cepheus above and to the east, Cassiopeia 
east, and Ursa Major west. In the Northeast, Perseus is just 
rising, while south of it Andromeda and Pegasus are fairly 
up. Alo7tg the Ecliptic, Aquarius is risen, next Capricornus, 
Sagittarius reaches to the meridian, Scorpio is just past, Libra 
next, and Virgo (Spica) just touches the horizon. North of 
the Ecliptic, Taurus Poniatowskii is on and Lyra is just east of 
the meridian ; the Swan and Dolphin are east of Lyra, Ser- 
pentarius and Hercules are above Scorpio, and just west of 
the meridian ; thence west are Corona and Bootes, while far 
in the northwest are Coma Berenices and Cor Caroli. 

September. (8 p. m.) — Draco is above and to the west 
of Polaris, Cepheus above and to the east, Cassiopeia east, 
Ursa Major is below and to the west. In the Northeast, Per- 
seus is just rising, hi the East, Andromeda is fairly up, Peg- 
asus is nearly midway to the meridian. Along the Ecliptic, 
Pisces is just rising, next Aquarius, Capricornus in the south- 
west, Sagittarius on the meridian in the south, next Scorpio 
in the southwest, Libra, and lastly Virgo just setting. North 
of the Ecliptic, Lyra is on the meridian, Cygnus, the Dolphin, 
and Aquila just to the east, while to the west are Taurus 
Poniatowski and Serpentarius; north of these latter are Her- 
cules, Corona, Bootes, Cor Caroli, and Coma Berenices. 

October. (7 p. m.) — In the North, Cepheus and Draco 
are above Polaris, Ursa Minor west, Cassiopeia east, and Ursa 
Major below and west. In the Northeast, Perseus is fairly 
risen. In the East, Andromeda is nearly midway to the ze- 
nith. Along the Ecliptic, Aries is just rising, Pisces well up, 
Aquarius and Capricornus in the southeast, Sagittarius in 
the south, Scorpio far down in the southwest, and Libra just 
setting. North of the Ecliptic, Cygnus and Aquila are on the 



334: GUIDE TO THE CONSTELLATIONS. 

meridian, the Dolphin just east of it, and far south ; Lyn^ \ 
west of the meridian, Taurus Poniatowski lower down and t» 
the south, Serpentarius is just above Scorpio ; next, in line 
with it and Polaris, is Hercules ; Corona and Bootes are toward 
the southwest, where Coma Berenices is just setting. 

November. (7 p. m.) — In the North, Ursa Major is below 
Polaris, Ursa Minor and Draco are to the west, Cepheus 
above, and Cassiopeia above and to the east. In the North- 
east, Auriga is just rising, and Perseus is above, nearly mid- 
way to the meridian. Along the Ecliptic, Taurus is just rising, 
next Aries and Pisces ; Aquarius is on the meridian, south ; 
then Capricornus, and lastly Sagittarius, in the southwest. 
North of the Ecliptic, Pegasus and Andromeda lie east of the 
meridian, the Swan, Dolphin, Eagle, Taurus Poniatowski, and 
Lyra west, hi the Northwest are Hercules and Corona. 

December. (7 p. m.) — hi the North, Cassiopeia is above 
Polaris, Cepheus above and to the west, Perseus above and 
to the east, Draco west, and Ursa Major below. In the 
Northeast, below Perseus, is Auriga. In the East, Orion is 
rising. Along the Ecliptic, Gemini is just rising, Taurus is 
nearly midway, next Aries, Pisces is on the meridian, then 
Aquarius, and lastly Capricornus, far in the southwest, hi the 
South, east of the meridian, is Cetus, and west is Fomalhaut. 
North of the Ecliptic, Andromeda is nearly on the meridian, 
and Pegasus west of it; Cygnus, Delphinus, Lyra, and Aquila 
are about midway, while Taurus Poniatowski is just sinking to 
the horizon. In the Northwest, Hercules is just setting. 

• 

Note.— It should be borne in mind that a month makes a variation of 
about two hours (30'') in the rise of a star : hence, in the foregoing " Guide," 
the '-January Skv" of 9 p. 3I. would be about the same as the "February- 
Sky" of T p. 31. : the ■• January Skv" of 11 p. 3i. would be about the same as 
the "March Sky" of 7 p. 3i., &c. In this way the "Guide" may be used for 
any hour in the*^ night. The pupil will see that in the '• Guide" the prominent 
figures and stars in each constellation are given in parentheses. Examples : 
the " Y" in Aquarius, the " scalene triangle"' in Aries. " Job's cofian" in the 
Dolphin, " Procyon" in Canis Minor, &c. These aid in identifying the con- 
stellation. 



INDEX. 



PAGE 

Aberration 135 

Aerolites 195 

Algol 243 

Aldebaran 247 

Amplitude 37 

Antinous 261 

Anaxagoras 17 

Andromeda 245 

Antares 260 

Apsides 128 

Apparent motion . . 99 

Arcturus 256 

Argo 264 

Arcturus 256 

Aries 246 

Auriga 248 

Azimuth 37 

Astrology 22 

Bailey's Beads 169 

Bellatrix 251 

Betelgeuse 251 

Bode's Law 173 

Bolides 196 

Bootes 256 

Berenice's Hair 255 

Cassiopeia 241 

Canis Major, Canis Minor 252 

Cancer 254 

Capricornus 261 

Castor and Pollnx 250 

Celestial Sphere 35 

Pole 38 

" Measurements 38 

" Chemistry 284 

Centaur 264 

Cepheus 241 

Cetus 249 

Chinese 26 

Chaldeans 17 

Colures 40 

Conjunctions 71, 75 

Cor Caroli 255 

Corona 259 

Comets 206 

Constellations 234 

Copernican System 23 

Cross 264 

Crystalline Spheres 18 

Cy gnus 262 

Declination 39 

Dipper 236 

Diurnal Motion 100 

Dolphin 262 

Draco 239 

Earth 96 

Earth-shine 144 

Eclipses 155 

Ecliptic 40, 109 

" Polesof 41 



PAGE 

Ecliptic, Obliquity of 110 

Egyptians 19 

Ellipse 68, 26 

Elongation 76 

•' (Measurements) 298 

Emersion 181 

Equinoxes- 113 

" Precession of 120 

Equinoctial 38 

Evening Stars 82 

Falling Stars 195 

Fixed Stars 222 

Names of. 227 

" Distanceof. 223 

" Motion of 223 

" Size of 226 

" Parallaxof 223 

Galileo 29 

Galaxy 280 

Gemini 249 

Geocentric 75 

Gibbous 146 

Golden Number 162 

Greek Alphabet 228 

Grecians 17 

Gravitation 34 

Harvest Moon 148 

Hare 251 

Hercules 257 

Herschel's Theory 281 

Heliocentric 75 

Horizon 37 

Hour Circles 38 

Hyades 247 

Hydra 255 

Immersion 181 

Irradiation 141 

Job's Coffin 252 

Jupiter 175 

Kepler's Laws 25 

KirchofiTs Theory 64 

Latitude 41 

Le Monnier 190 

Le Verrier 193 

Leo 253 

Libra 260 

Linnjeus 152 

Librations : 142 

Lyra 263 

Mars 168 

Meteors 194 

Mean day 293 

Mercury S3 

Meteoric Cycle 161 

Milky Way 280 



336 



INDEX. 



PAGE 

Minor Planets 172 

Moon 139 

" Eclipse of. 162 

Nadir 37 

Naos 252 

Newton 31 

Nebular Hypothesis 2S2 

NebuliB 266 

Neptune 191 

Noon-mark 291 

North Polar Star 237 

Nodes 69, 149 

" Longitude 69 

" Line of 69 

Orbits of Planets 66 

" Stars 104 

Occultation 149 

Orion 251 

Parallax 137 

" of stars 222 

Penumbra 155 

Perseus 243 

Pesasu 8 245 

Pisces 24S 

Phases 78 

Planet^. 65 

Pleiadt ;« 247 

Polaris 237 

Polar S(ar 237 

" Slars, South 56,260 

" d.fitance 39 

Procvoi; 252 

Precessi >n 120 

Ptolemac Theory 20 

Pjthago.-as .. 18 

Quadrature 76 

Refraction 130 

Retrograde motion 77, 79 

Regulus 253 

Right ascension 39 

Saros 160 

Saturn 182 

Sigittarius 261 

Scorpio 260 

Scintillation 226 

Signs of Zodiac 42, 230 

Seasons 110 



FACE 

Serpentarius 259 

Shooting Stars 194 

Sirius 252 

Sidereal Revolution 55, 80 

Southern Fish 261 

Solstices 41, 114 

Solar time 289 

Solar System 45 

Spectrum Analysis 284 

Spica 257 

Sun 46 

" Path of 108 

" Change in form and place of 1.31 

" Spots 50 

Stars 221 

" Number of. 224 

" Size 226 

" Distance 223 

" Colored 266 

" Variable 267 

" Temporary 268 

Double 265 

Syzygies 166 

Synodic 55, 80 

Taurus 247 

Poniatowskii 260 

Tides 165 

Time 288 

Transit 77 

Triangles 246 

Tvcho Brahe 24 

Twilight 133 

Umbra 155 

Uranus 189 

Ursa Maior 235 

" Minor 237 

Vega , 262 

Venus 82 

Vertical Circle 37 

Velocity of Light 182 

Vi rgo 254 

Vulcan 82 

Whale 249 

Wilson's Theory 62 

Zenith 37 

Zodiac 41 

Zodiacal Light 817 



g^H p^u, nU pamwris, mu\ all ®imf<s. 



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